An extreme analysis for the 2010 precipitation event at the south of Saskatchewan prairie

After a prolonged drought period in the early 2000s, the Canadian prairie experienced a remarkably wet year in 2010. Five stations near the edge of the Saskatchewan boreal forest recorded historically high cumulative precipitation (from April to September). The exceptional wet year causes the public concerns on flood controls and land use management in the region. Using the Canadian National Climate Data Achieve, characteristics of six-month cumulative precipitation sums over Saskatchewan prairie are investigated by the Generalised Extreme Value (GEV) Theory. Based on the unconstrained GEV distribution, the 2010 event is outside the estimated 95% confidence intervals for the five Canadian prairie stations. On the contrary, the exceptional high 2010 cumulative perception sums for the five stations are still bounded by the estimated confidence bounds if the GEV distribution is constrained to the Gumbel distribution (i.e. setting the shape factor of the GEV distribution to be zero). These results demonstrate that the classical extreme analysis is useful for planning unprecedented extreme events in the Canadian Prairie, if the GEV distribution is constrained to the Gumbel distribution with the estimated uncertainty bounds based on the order statistics. © 2012 Global NEST Printed in Greece. All rights reserved

A restatement of the natural science evidence concerning catchment-based "natural” flood management in the United Kingdom

Flooding is a very costly natural hazard in Great Britain and is expected to increase further under future climate change scenarios. Flood defences are commonly deployed to protect communities and property from flooding, but in recent years flood management policy has looked towards solutions that seek to mitigate flood risk at flood-prone sites through targeted interventions throughout the catchment, sometimes using techniques which involve working with natural processes. This paper describes a project to provide a succinct summary of the natural science evidence base concerning the effectiveness of catchment-based “natural” flood management in the United Kingdom. The evidence summary is designed to be read by an informed but not technically-specialist audience. Each evidence statement is placed into one of four categories describing the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material

An assessment of the ability of Bartlett–Lewis type of rainfall models to reproduce drought statistics

Of all natural disasters, the economic and environmental consequences of droughts are among the highest because of their longevity and widespread spatial extent. Because of their extreme behaviour, studying droughts generally requires long time series of historical climate data. Rainfall is a very important variable for calculating drought statistics, for quantifying historical droughts or for assessing the impact on other hydrological (e. g. water stage in rivers) or agricultural (e. g. irrigation requirements) variables. Unfortunately, time series of historical observations are often too short for such assessments. To circumvent this, one may rely on the synthetic rainfall time series from stochastic point process rainfall models, such as Bartlett-Lewis models. The present study investigates whether drought statistics are preserved when simulating rainfall with Bartlett-Lewis models. Therefore, a 105 yr 10 min rainfall time series obtained at Uccle, Belgium is used as a test case. First, drought events were identified on the basis of the Effective Drought Index (EDI), and each event was characterized by two variables, i.e. drought duration (D) and drought severity (S). As both parameters are interdependent, a multivariate distribution function, which makes use of a copula, was fitted. Based on the copula, four types of drought return periods are calculated for observed as well as simulated droughts and are used to evaluate the ability of the rainfall models to simulate drought events with the appropriate characteristics. Overall, all Bartlett-Lewis model types studied fail to preserve extreme drought statistics, which is attributed to the model structure and to the model stationarity caused by maintaining the same parameter set during the whole simulation period

Integrated management of water resource systems under changing water availability, policy, and irrigation expansion plans

Conventional water resource management has been based on the assumption of stationarity in the characteristics of the water resource systems. However, the validity of this assumption is questionable due to changing climate and increasing human activities. The current level of uncertainty inherent in the projection of future natural and anthropogenic conditions has also complicated water resource planning and management. As a result, there is a fundamental need to acknowledge the uncertainty associated with water resource systems and propose improved management schemes under uncertainty. This thesis presents three developments to assist in understanding system behavior under historical and changing conditions, and to propose an alternative framework for decision making under uncertain conditions. The three parts are put together and applied to the Saskatchewan River Basin (SaskRB) in Saskatchewan, which is a strategically important water resource system in western Canada. In brief, first a Sustainability-oriented Water allocation, Management, and Planning (SWAMPSK) model is developed using the System Dynamics approach. This water resource model captures the causal relationships among system components and combines various aspects of the water resource system, such as water allocation, irrigation demand, and economic evaluation within an integrated system. Second, SWAMPSK is used to map the vulnerability and sectorial trade-offs in the SaskRB in Saskatchewan under changing water availability and irrigation expansion. Using a bottom-up approach, a wide range of streamflow conditions is stochastically generated to accommodate likely scenarios of change in water availability. The streamflow ensemble and alternative irrigation expansion scenarios are used in SWAMPSK for evaluating the water resource system’s performance under potential changes in natural conditions and irrigated areas. Third, an innovative probabilistic framework is proposed to evaluate the risk in system behavior under changing conditions and to identify the contributions of various changing conditions on the overall system performance. For this purpose, the empirical probability distributions of system performance are used to quantify the individual and joint impacts of changing conditions on the system performance with the goal of proposing policies that minimize the risk of undesired changes in system. This thesis provides a set of new and strategically-important insights to the water resource system in Saskatchewan. In brief, increase in irrigation area can raise the total economic benefit except in extremely dry flow conditions, but with some cost of decreasing water availability in downstream regions. Saskatchewan can meet the inter-provincial commitment under changes in flow regime and irrigation expansion. Results also show that no one specific policy can provide the optimal option for water resource management under all changing flow and irrigation expansion conditions and the joint impacts of changing water availability, policy, and irrigation expansion are complex nonlinear functions of individual drivers. This thesis also offers a set of new modeling tools that can be used to assist decision making under uncertainty. In particular, the proposed risk-based framework allows an explicit understanding of the variations in the system performance as a result of changing natural and/or anthropogenic conditions and can be transferred to decision making applications

High-frequency monitoring of nitrogen and phosphorus response in three rural catchments to the end of the 2011–2012 drought in England

This paper uses high-frequency bankside measurements from three catchments selected as part of the UK government-funded Demonstration Test Catchments (DTC) project. We compare the hydrological and hydrochemical patterns during the water year 2011–2012 from the Wylye tributary of the River Avon with mixed land use, the Blackwater tributary of the River Wensum with arable land use and the Newby Beck tributary of the River Eden with grassland land use. The beginning of the hydrological year was unusually dry and all three catchments were in states of drought. A sudden change to a wet summer occurred in April 2012 when a heavy rainfall event affected all three catchments. The year-long time series and the individual storm responses captured by in situ nutrient measurements of nitrate and phosphorus (total phosphorus and total reactive phosphorus) concentrations at each site reveal different pollutant sources and pathways operating in each catchment. Large storm-induced nutrient transfers of nitrogen and or phosphorus to each stream were recorded at all three sites during the late April rainfall event. Hysteresis loops suggested transport-limited delivery of nitrate in the Blackwater and of total phosphorus in the Wylye and Newby Beck, which was thought to be exacerbated by the dry antecedent conditions prior to the storm. The high rate of nutrient transport in each system highlights the scale of the challenges faced by environmental managers when designing mitigation measures to reduce the flux of nutrients to rivers from diffuse agricultural sources. It also highlights the scale of the challenge in adapting to future extreme weather events under a changing climate

Pang and Lambourn Hydrometric Review 2009

This Review covers the streamflow, soil water, groundwater and weather data collected from the hydrological infrastructure networks in the Pang and Lambourn catchments. The period covered here is primarily for the calendar year 2009, but because the dataset extends back nearly a decade the earlier years are included in some of the graphs and accompanying text to provide a longer term context

Characterization of process-oriented hydrologic model behavior with temporal sensitivity analysis for flash floods in Mediterranean catchments

This paper presents a detailed analysis of 10 flash flood events in the Mediterranean region using the distributed hydrological model MARINE. Characterizing catchment response during flash flood events may provide new and valuable insight into the dynamics involved for extreme catchment response and their dependency on physiographic properties and flood severity. The main objective of this study is to analyze flash-flood-dedicated hydrologic model sensitivity with a new approach in hydrology, allowing model outputs variance decomposition for temporal patterns of parameter sensitivity analysis. Such approaches enable ranking of uncertainty sources for nonlinear and nonmonotonic mappings with a low computational cost. Hydrologic model and sensitivity analysis are used as learning tools on a large flash flood dataset. With Nash performances above 0.73 on average for this extended set of 10 validation events, the five sensitive parameters of MARINE process-oriented distributed model are analyzed. This contribution shows that soil depth explains more than 80% of model output variance when most hydrographs are peaking. Moreover, the lateral subsurface transfer is responsible for 80% of model variance for some catchment-flood events’ hydrographs during slow-declining limbs. The unexplained variance of model output representing interactions between parameters reveals to be very low during modeled flood peaks and informs that model parsimonious parameterization is appropriate to tackle the problem of flash floods. Interactions observed after model initialization or rainfall intensity peaks incite to improve water partition representation between flow components and initialization itself. This paper gives a practical framework for application of this method to other models, landscapes and climatic conditions, potentially helping to improve processes understanding and representation