1] Increasing availability of ensemble outputs from general circulation models (GCMs) and regiona... more 1] Increasing availability of ensemble outputs from general circulation models (GCMs) and regional climate models (RCMs) permits fuller examination of the implications of climate uncertainties in hydrological systems. A Bayesian statistical framework is used to combine projections by weighting and to generate probability distributions of local climate change from an ensemble of RCM outputs. A stochastic weather generator produces corresponding daily series of rainfall and potential evapotranspiration, which are input into a catchment rainfall-runoff model to estimate future water abstraction availability. The method is applied to the Thames catchment in the United Kingdom, where comparison with previous studies shows that different downscaling methods produce significantly different flow predictions and that this is partly attributable to potential evapotranspiration predictions. An extended sensitivity test exploring the effect of the weights and assumptions associated with combining climate model projections illustrates that under all plausible assumptions the ensemble implies a significant reduction in catchment water resource availability.
Assessing the potential impacts of climatic change on flood frequency is a key research topic wit... more Assessing the potential impacts of climatic change on flood frequency is a key research topic within the United Kingdom. Current methods tend to focus on continuous simulation, where a catchment model is calibrated for the observed flow time-series record and then the input climatic data is perturbed to represent a physically realistic future climate scenario. This project aims to develop an alternative approach, tentatively named ‘frequency curve mapping'. This involves mapping from rainfall frequency to flood frequency using supporting information such as estimates of antecedent conditions and physical catchment descriptors. The project is part of a larger study known as "a next generation national Flood Risk Assessment under Climate ChAnge Scenarios" (FRACAS), funded under the National Environmental Research Councils (NERC) Flood Risk from Extreme Events (FREE) programme. Early work used event based analysis to look at how consistent estimates of a storm and antecedent conditions might be used to estimate peak flow in a wide range of catchments. This has been carried out for a set of around 500 catchments within the UK, representing a wide variety of hydrological regimes. Results indicate that certain types of catchments are suited to estimating peak flow in this way. Groundwater dominated catchments display the poorest performance in flow estimation due to the relative importance of groundwater levels in influencing antecedent conditions in these types of catchments. In these cases, the antecedent conditions are considered complex and cannot be captured using a simple antecedent precipitation index or soil moisture estimate. Surface water catchments tend to be more amenable to the use of simple antecedent estimates. In order to assess performance in flow estimation, events were classified seasonally and by magnitude. Catchments have also been classified using numerous physical descriptors. This early work informed the selection of a catchment set which can now be used to develop a direct link between a rainfall frequency and flood frequency curve. This is currently being carried out on a small subset of the original catchments. Using only the biggest rainfall events in a catchments rainfall record, the basic assumption is made that for these events, the antecedent influences are negligible. In these catchments, the comparison of growth factors for the largest rainfall and associated flow events can be made without any modification of the storm. Where antecedent influences are suspected, the storm total must be modified. This work is currently on-going. Future work will likely involve extending to a larger catchment set, and also to the use of future rainfall scenarios to consider the climate change impacts.
Abstract The vertical and horizontal spatial variations in key climate variables govern the runof... more Abstract The vertical and horizontal spatial variations in key climate variables govern the runoff contributions of the Upper Indus Basin's (UIB) various elevation zones and sub-catchments. This complex mountainous region's observed patterns of climate variation, highly diverse by season and parameter, do not match general global trends. This study applies and compares data from ground based and remote sensing sources to assess more reliably the patterns of temperature (lapse rate) and precipitation with elevation.
[1] The nonhomogeneous spatial activation of raincells (NSAR) model is presented which provides a... more [1] The nonhomogeneous spatial activation of raincells (NSAR) model is presented which provides a continuous spatial-temporal stochastic simulation of rainfall exhibiting spatial nonstationarity in both amounts and occurrence. Spatial nonstationarity of simulated rainfall is important for hydrological modeling of mountainous catchments where orographic effects on precipitation are strong. Such simulated rainfall fields support the current trend toward distributed hydrological modeling.
Abstract The UP (Upscaled Physically-based) hydrological modelling system to the Arkansas-Red Riv... more Abstract The UP (Upscaled Physically-based) hydrological modelling system to the Arkansas-Red River basin (USA) is designed for macroscale simulations of land surface processes, and aims for a physical basis and, avoids the use of discharge records in the direct calibration of parameters.
[2] Large ensembles of climate model outputs provide the potential to explore some of the uncerta... more [2] Large ensembles of climate model outputs provide the potential to explore some of the uncertainties in modelbased predictions of future climate at both global and regional scales.
Abstract. The purpose of this paper is to provide a method for perturbing Weather Generators (WGs... more Abstract. The purpose of this paper is to provide a method for perturbing Weather Generators (WGs) for future decades and to assess its effectiveness. Here the procedure is applied to the WG implemented within the UKCP09 package and assessed using data from a Regional Climate Model (RCM) simulation which provides a significant “climate change” between a control run period and a distant future. The WG is normally calibrated on observed data.
Abstract Satellite altimetry is routinely used to provide levels for oceans or large inland water... more Abstract Satellite altimetry is routinely used to provide levels for oceans or large inland water bodies from space. By utilizing retracking schemes specially designed for inland waters, meaningful river stages can also be recovered when standard techniques fail. Utilizing retracked waveforms from ERS-2 and ENVISAT along the Mekong, comparisons against observed stage measurements show that the altimetric measurements have a root mean square error (RMSE) of 0· 44–0· 65 m for ENVISAT and 0· 46–0· 76 m for ERS-2.
During the last decade, there have been increasing concerns over water resource drought in northe... more During the last decade, there have been increasing concerns over water resource drought in northern England, brought about by the 1995 Yorkshire drought with an estimated 5-month rainfall return period of 200 years. The impacts of climatic change and variability on water resource reliability, resilience, and vulnerability in this region are examined by modeling changes to weather type frequency, mean rainfall statistics, and potential evapotranspiration.
Further developments of a stochastic rainfall model conditioned by weather types for the water re... more Further developments of a stochastic rainfall model conditioned by weather types for the water resource region of Yorkshire, UK, are presented. The model is extended to multi-site and a new technique is developed to allow the reproduction of historical monthly rainfall cross-correlation statistics. Monte–Carlo simulation and sampling techniques are combined to preserve monthly historical rainfall cross-correlation between two sub-regional Neyman–Scott Rectangular Pulses (NSRP) rainfall models.
Abstract Measurements of water-vapour continuum absorption in the 10-12 μm window have been made ... more Abstract Measurements of water-vapour continuum absorption in the 10-12 μm window have been made in the tropical atmosphere using a multi-channel narrow field-of-view radiometer mounted on an aircraft. Comparisons with two radiative transfer models (GENLN 2 and LOWTRAN7) are made which show that the model underestimates the absorption by some thirty percent.
Abstract A stochastic model is developed for the synthesis of daily precipitation using condition... more Abstract A stochastic model is developed for the synthesis of daily precipitation using conditioning by weather types. Daily precipitation statistics at multiple sites within the region of Yorkshire, UK, are linked to objective Lamb weather types (LWTs) and used to split the region into three distinct precipitation sub-regions. Using a variance minimisation criterion, the 27 LWTs are clustered into three physically realistic groups or'states'.
Abstract Variations in precipitation in Yorkshire, UK, are linked to large-scale atmospheric circ... more Abstract Variations in precipitation in Yorkshire, UK, are linked to large-scale atmospheric circulation using the North Atlantic Oscillation (NAO) index, objective Lamb weather types, and long-term seasonal and annual precipitation indices at seven sites. Since the 1960s, a significant decrease in summer precipitation has been observed across the region, with increasing winter precipitation at western locations since 1970.
[1] Future projections from climate models and recent observations show a worldwide increase in b... more [1] Future projections from climate models and recent observations show a worldwide increase in both the frequency and intensity of heavy rainfall, coinciding with widespread flooding and landslides in Europe. It is estimated, using regional frequency analysis, that the magnitude of extreme rainfall has increased two-fold over parts of the UK since the 1960s. Intensities previously experienced, on average, every 25 years now occur at 6 year intervals; a consequence of both increased event frequency and changes in seasonality.
Abstract Multi-day rainfall events are an important cause of recent severe flooding in the UK, an... more Abstract Multi-day rainfall events are an important cause of recent severe flooding in the UK, and any change in the magnitude of such events may have severe impacts upon urban structures such as dams, urban drainage systems and flood defences and cause failures to occur.
Abstract General circulation models (GCMs), or stand-alone models that are forced by the output f... more Abstract General circulation models (GCMs), or stand-alone models that are forced by the output from GCMs, are increasingly being used to simulate the interactions between snow cover, snowmelt, climate and water resources. The variation in snowpack extent, and hence albedo, through time in a cell is likely to be substantial, especially in mid-latitude mountainous regions. As a consequence, the energy budget simulation by a GCM relies on a realistic representation of snowpack extent.
The Generalised Neyman-Scott Rectangular Pulses (GNSRP) model (Cowpertwait, 1994; 1995) is one of... more The Generalised Neyman-Scott Rectangular Pulses (GNSRP) model (Cowpertwait, 1994; 1995) is one of the most advanced approaches to stochastic rainfall simulation currently available. The model has been implemented in software at Newcastle University (UNEW) known as RainSim, which has been built in order to provide a state-of-the-art rainfall simulator for a variety of applications and to act as a sound basis for further research into rainfall modelling.
Abstract Now and in the future, the flows of the Upper Indus Basin (UIB) are and will be depended... more Abstract Now and in the future, the flows of the Upper Indus Basin (UIB) are and will be depended upon by hundreds of millions of people for their food security and economic livelihoods. Communities in the headwater reaches of the UIB—which contribute the bulk of runoff for the basin—are equally deserving of improved living conditions, but often lag behind downstream communities in benefitting from infrastructure.
This paper describes the development of a weather generator for use in climate impact assessments... more This paper describes the development of a weather generator for use in climate impact assessments of agricultural and water system management. The generator produces internally consistent series of meteorological variables including: rainfall, temperature, humidity, wind, sunshine, as well as derivation of potential evapotranspiration.
Abstract New predictive methodologies are needed to support sustainable catchment management, par... more Abstract New predictive methodologies are needed to support sustainable catchment management, particularly in poorly gauged or ungauged basins. The CHASM research programme has been established to gain new understanding of the hydrological and ecological functioning of mesoscale catchments (102–103 km2) and of how catchment response changes with scale, and to translate this new knowledge into enhanced predictive capability.
1] Increasing availability of ensemble outputs from general circulation models (GCMs) and regiona... more 1] Increasing availability of ensemble outputs from general circulation models (GCMs) and regional climate models (RCMs) permits fuller examination of the implications of climate uncertainties in hydrological systems. A Bayesian statistical framework is used to combine projections by weighting and to generate probability distributions of local climate change from an ensemble of RCM outputs. A stochastic weather generator produces corresponding daily series of rainfall and potential evapotranspiration, which are input into a catchment rainfall-runoff model to estimate future water abstraction availability. The method is applied to the Thames catchment in the United Kingdom, where comparison with previous studies shows that different downscaling methods produce significantly different flow predictions and that this is partly attributable to potential evapotranspiration predictions. An extended sensitivity test exploring the effect of the weights and assumptions associated with combining climate model projections illustrates that under all plausible assumptions the ensemble implies a significant reduction in catchment water resource availability.
Assessing the potential impacts of climatic change on flood frequency is a key research topic wit... more Assessing the potential impacts of climatic change on flood frequency is a key research topic within the United Kingdom. Current methods tend to focus on continuous simulation, where a catchment model is calibrated for the observed flow time-series record and then the input climatic data is perturbed to represent a physically realistic future climate scenario. This project aims to develop an alternative approach, tentatively named ‘frequency curve mapping'. This involves mapping from rainfall frequency to flood frequency using supporting information such as estimates of antecedent conditions and physical catchment descriptors. The project is part of a larger study known as "a next generation national Flood Risk Assessment under Climate ChAnge Scenarios" (FRACAS), funded under the National Environmental Research Councils (NERC) Flood Risk from Extreme Events (FREE) programme. Early work used event based analysis to look at how consistent estimates of a storm and antecedent conditions might be used to estimate peak flow in a wide range of catchments. This has been carried out for a set of around 500 catchments within the UK, representing a wide variety of hydrological regimes. Results indicate that certain types of catchments are suited to estimating peak flow in this way. Groundwater dominated catchments display the poorest performance in flow estimation due to the relative importance of groundwater levels in influencing antecedent conditions in these types of catchments. In these cases, the antecedent conditions are considered complex and cannot be captured using a simple antecedent precipitation index or soil moisture estimate. Surface water catchments tend to be more amenable to the use of simple antecedent estimates. In order to assess performance in flow estimation, events were classified seasonally and by magnitude. Catchments have also been classified using numerous physical descriptors. This early work informed the selection of a catchment set which can now be used to develop a direct link between a rainfall frequency and flood frequency curve. This is currently being carried out on a small subset of the original catchments. Using only the biggest rainfall events in a catchments rainfall record, the basic assumption is made that for these events, the antecedent influences are negligible. In these catchments, the comparison of growth factors for the largest rainfall and associated flow events can be made without any modification of the storm. Where antecedent influences are suspected, the storm total must be modified. This work is currently on-going. Future work will likely involve extending to a larger catchment set, and also to the use of future rainfall scenarios to consider the climate change impacts.
Abstract The vertical and horizontal spatial variations in key climate variables govern the runof... more Abstract The vertical and horizontal spatial variations in key climate variables govern the runoff contributions of the Upper Indus Basin's (UIB) various elevation zones and sub-catchments. This complex mountainous region's observed patterns of climate variation, highly diverse by season and parameter, do not match general global trends. This study applies and compares data from ground based and remote sensing sources to assess more reliably the patterns of temperature (lapse rate) and precipitation with elevation.
[1] The nonhomogeneous spatial activation of raincells (NSAR) model is presented which provides a... more [1] The nonhomogeneous spatial activation of raincells (NSAR) model is presented which provides a continuous spatial-temporal stochastic simulation of rainfall exhibiting spatial nonstationarity in both amounts and occurrence. Spatial nonstationarity of simulated rainfall is important for hydrological modeling of mountainous catchments where orographic effects on precipitation are strong. Such simulated rainfall fields support the current trend toward distributed hydrological modeling.
Abstract The UP (Upscaled Physically-based) hydrological modelling system to the Arkansas-Red Riv... more Abstract The UP (Upscaled Physically-based) hydrological modelling system to the Arkansas-Red River basin (USA) is designed for macroscale simulations of land surface processes, and aims for a physical basis and, avoids the use of discharge records in the direct calibration of parameters.
[2] Large ensembles of climate model outputs provide the potential to explore some of the uncerta... more [2] Large ensembles of climate model outputs provide the potential to explore some of the uncertainties in modelbased predictions of future climate at both global and regional scales.
Abstract. The purpose of this paper is to provide a method for perturbing Weather Generators (WGs... more Abstract. The purpose of this paper is to provide a method for perturbing Weather Generators (WGs) for future decades and to assess its effectiveness. Here the procedure is applied to the WG implemented within the UKCP09 package and assessed using data from a Regional Climate Model (RCM) simulation which provides a significant “climate change” between a control run period and a distant future. The WG is normally calibrated on observed data.
Abstract Satellite altimetry is routinely used to provide levels for oceans or large inland water... more Abstract Satellite altimetry is routinely used to provide levels for oceans or large inland water bodies from space. By utilizing retracking schemes specially designed for inland waters, meaningful river stages can also be recovered when standard techniques fail. Utilizing retracked waveforms from ERS-2 and ENVISAT along the Mekong, comparisons against observed stage measurements show that the altimetric measurements have a root mean square error (RMSE) of 0· 44–0· 65 m for ENVISAT and 0· 46–0· 76 m for ERS-2.
During the last decade, there have been increasing concerns over water resource drought in northe... more During the last decade, there have been increasing concerns over water resource drought in northern England, brought about by the 1995 Yorkshire drought with an estimated 5-month rainfall return period of 200 years. The impacts of climatic change and variability on water resource reliability, resilience, and vulnerability in this region are examined by modeling changes to weather type frequency, mean rainfall statistics, and potential evapotranspiration.
Further developments of a stochastic rainfall model conditioned by weather types for the water re... more Further developments of a stochastic rainfall model conditioned by weather types for the water resource region of Yorkshire, UK, are presented. The model is extended to multi-site and a new technique is developed to allow the reproduction of historical monthly rainfall cross-correlation statistics. Monte–Carlo simulation and sampling techniques are combined to preserve monthly historical rainfall cross-correlation between two sub-regional Neyman–Scott Rectangular Pulses (NSRP) rainfall models.
Abstract Measurements of water-vapour continuum absorption in the 10-12 μm window have been made ... more Abstract Measurements of water-vapour continuum absorption in the 10-12 μm window have been made in the tropical atmosphere using a multi-channel narrow field-of-view radiometer mounted on an aircraft. Comparisons with two radiative transfer models (GENLN 2 and LOWTRAN7) are made which show that the model underestimates the absorption by some thirty percent.
Abstract A stochastic model is developed for the synthesis of daily precipitation using condition... more Abstract A stochastic model is developed for the synthesis of daily precipitation using conditioning by weather types. Daily precipitation statistics at multiple sites within the region of Yorkshire, UK, are linked to objective Lamb weather types (LWTs) and used to split the region into three distinct precipitation sub-regions. Using a variance minimisation criterion, the 27 LWTs are clustered into three physically realistic groups or'states'.
Abstract Variations in precipitation in Yorkshire, UK, are linked to large-scale atmospheric circ... more Abstract Variations in precipitation in Yorkshire, UK, are linked to large-scale atmospheric circulation using the North Atlantic Oscillation (NAO) index, objective Lamb weather types, and long-term seasonal and annual precipitation indices at seven sites. Since the 1960s, a significant decrease in summer precipitation has been observed across the region, with increasing winter precipitation at western locations since 1970.
[1] Future projections from climate models and recent observations show a worldwide increase in b... more [1] Future projections from climate models and recent observations show a worldwide increase in both the frequency and intensity of heavy rainfall, coinciding with widespread flooding and landslides in Europe. It is estimated, using regional frequency analysis, that the magnitude of extreme rainfall has increased two-fold over parts of the UK since the 1960s. Intensities previously experienced, on average, every 25 years now occur at 6 year intervals; a consequence of both increased event frequency and changes in seasonality.
Abstract Multi-day rainfall events are an important cause of recent severe flooding in the UK, an... more Abstract Multi-day rainfall events are an important cause of recent severe flooding in the UK, and any change in the magnitude of such events may have severe impacts upon urban structures such as dams, urban drainage systems and flood defences and cause failures to occur.
Abstract General circulation models (GCMs), or stand-alone models that are forced by the output f... more Abstract General circulation models (GCMs), or stand-alone models that are forced by the output from GCMs, are increasingly being used to simulate the interactions between snow cover, snowmelt, climate and water resources. The variation in snowpack extent, and hence albedo, through time in a cell is likely to be substantial, especially in mid-latitude mountainous regions. As a consequence, the energy budget simulation by a GCM relies on a realistic representation of snowpack extent.
The Generalised Neyman-Scott Rectangular Pulses (GNSRP) model (Cowpertwait, 1994; 1995) is one of... more The Generalised Neyman-Scott Rectangular Pulses (GNSRP) model (Cowpertwait, 1994; 1995) is one of the most advanced approaches to stochastic rainfall simulation currently available. The model has been implemented in software at Newcastle University (UNEW) known as RainSim, which has been built in order to provide a state-of-the-art rainfall simulator for a variety of applications and to act as a sound basis for further research into rainfall modelling.
Abstract Now and in the future, the flows of the Upper Indus Basin (UIB) are and will be depended... more Abstract Now and in the future, the flows of the Upper Indus Basin (UIB) are and will be depended upon by hundreds of millions of people for their food security and economic livelihoods. Communities in the headwater reaches of the UIB—which contribute the bulk of runoff for the basin—are equally deserving of improved living conditions, but often lag behind downstream communities in benefitting from infrastructure.
This paper describes the development of a weather generator for use in climate impact assessments... more This paper describes the development of a weather generator for use in climate impact assessments of agricultural and water system management. The generator produces internally consistent series of meteorological variables including: rainfall, temperature, humidity, wind, sunshine, as well as derivation of potential evapotranspiration.
Abstract New predictive methodologies are needed to support sustainable catchment management, par... more Abstract New predictive methodologies are needed to support sustainable catchment management, particularly in poorly gauged or ungauged basins. The CHASM research programme has been established to gain new understanding of the hydrological and ecological functioning of mesoscale catchments (102–103 km2) and of how catchment response changes with scale, and to translate this new knowledge into enhanced predictive capability.
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Papers by Chris Kilsby