Modelling the hydrological impacts of climate change on UK lowland wet grassland

Abstract

Hydrological impacts of climate change upon the Elmley Marshes, southeast England, are simulated using a coupled hydrological/hydraulic model developed using MIKE SHE/MIKE 11 and calibrated to contemporary conditions. Predicted changes in precipitation, temperature, radiation and wind speed from the UK Climate Impacts Programme associated with four emissions scenarios for the 2050s are used to modify precipitation and potential evapotranspiration data. For each emissions scenario two sets of potential evapotranspiration data are derived, one using changes in temperature (PET temp ), the other incorporating changes in temperature, radiation and wind speed (PET trws ). Results indicate drier conditions through the progressively higher emissions scenarios when compared to contemporary conditions. Changes are particularly pronounced when using PET trws . Summer water tables are lower (PET temp 0.01-0.08 m; PET trws 0.07-0.27 m) and the duration of high winter water tables is reduced. Although water tables still intercept the surface in winter when using PET temp , this ceases when PET trws is employed. Summer ditch water levels for the PET temp scenarios are lower (0.01-0.21 m) and in dry winters they do not reach mean field level. Under the PET trws scenarios summer and winter ditch water levels are lower by on average 0.21 m and 0.30 m respectively. Levels never reach the elevation of the marsh surface. Lower groundwater and ditch water levels result in declines in the magnitude and duration of surface inundation which is virtually eliminated with the PET trws scenarios. Hydrological changes can be expected to have ecological impacts which may include the loss of some grassland species adapted to periods of high water table. Reductions in the extent of surface water in spring, especially for the PET trws scenarios, are likely to reduce suitability for wading birds including lapwing (Vanellus vanellus) and redshank (Tringa totanus) for which the marshes are internationally renowned.

Large-scale regionalization of water table depth in peatlands optimized for greenhouse gas emission upscaling

“…Their suitability is strongly related to data availability, which very often decreases in quality and spatial density with increasing scale of the study area. Spatially distributed process-based modeling (Thompson et al, 2009) and semiphysical statistical approaches (Bierkens and Stroet, 2007) are able to reproduce well the water level dynamics in wetlands environments including peatlands. However, they heavily rely on spatial information about the system's physical properties and boundary conditions (peat hydraulic properties, hydraulic conductivity of peat base, drainage system), data that is often only available with sufficient detail at a regional scale (Limpens et al, 2008).…”

“…It is crucial that there is little or no hydraulic resistance by a low conductive layer between the perforated part of the monitoring well and the fluctuating water level. If hydraulic resistance is too high, the monitoring well acts as a piezometer and water levels may substantially differ from the actual phreatic level as shown for peatlands by van der Gaast et al (2009). If such piezometer data is part of a data set and interpreted as phreatic water level data during model calibration, this can lead to an under-or overestimation of predicted water levels in organic soils.…”

Modelling the impact of prescribed global warming on runoff from headwater catchments of the Irrawaddy River and their implications for the water level regime of Loktak Lake, northeast India

“…This approach has been widely used to assess C. R. Singh et al: Impact of prescribed global warming on Loktak Lake climate change impacts on river and wetland hydrological regimes (e.g. Chiew et al, 1995;Fowler and Kilsby, 2007;Thompson et al, 2009) and is adopted by the other papers in this special issue. It involves the following stages (Arnell and Reynard, 1996): (i) define, calibrate and validate a model of the hydrological system using current climate data; (ii) define climate change scenarios and perturb the original input climate data accordingly; and (iii) run the hydrological model with these perturbed climate data and compare results with those simulated under current ("baseline") conditions.…”

“…These data were used to calculate monthly Hargreaves PET and, in turn, mean monthly precipitation and evapotranspiration over the thirty year scenario period. The differences between mean monthly precipitation and evapotranspiration for the baseline period and each scenario, when expressed as a percent, defined delta factors by which the original station data employed within the calibrated models were modified (see Thompson et al, 2009). These perturbed meteorological inputs were subsequently used within the three MIKE SHE models of Loktak Lake sub-catchments and the resulting discharges used to re-evaluate discharges for ungauged sub-catchments using the method described above.…”

“…Hartig et al, 1997;Mortsch, 1998;Conly and van der Kamp, 2001). Many freshwater wetlands are particularly vulnerable to climate change induced modifications to hydrological regimes due to the delicate balance between precipitation and evaporation (Clair, 1998;Thompson et al, 2009). For example, the surface areas of both Lake Chad, West Africa (Talling and Lamoalle, 1998) and Qinghai Lake, China (Bates et al, 2008) have declined following reduced catchment precipitation and in turn smaller inflows from contributory rivers.…”