Julian R. Thompson

Uncertainty in the estimation of potential evapotranspiration under climate change

21st century climate change is projected to result in an intensification of the global hydrological cycle, but there is substantial uncertainty in how this will impact freshwater availability. A relatively overlooked aspect of this uncertainty pertains to how different methods of estimating potential evapotranspiration (PET) respond to changing climate. Here we investigate the global response of six different PET methods to a 2 degrees C rise in global mean temperature. All methods suggest an increase in PET associated with a warming climate. However, differences in PET climate change signal of over 100% are found between methods. Analysis of a precipitation/PET aridity index and regional water surplus indicates that for certain regions and GCMs, choice of PET method can actually determine the direction of projections of future water resources. As such, method dependence of the PET climate change signal is an important source of uncertainty in projections of future freshwater availability. Citation: Kingston, D. G., M. C. Todd, R. G. Taylor, J. R. Thompson, and N. W. Arnell (2009), Uncertainty in the estimation of potential evapotranspiration under climate change, Geophys. Res. Lett., 36, L20403, doi: 10.1029/2009GL040267.

The impact of climate change on groundwater recharge and runoff in a humid, equatorial catchment: sensitivity of projections to rainfall intensity

Abstract Projected warming in equatorial Africa, accompanied by greater evaporation and more frequent heavy precipitation events, may have substantial but uncertain impacts on terrestrial hydrology. Quantitative analyses of climate change impacts on catchment hydrology require high-resolution (<50 km) climate data provided by regional climate models (RCMs). We apply validated precipitation and temperature data from the RCM PRECIS (Providing Regional Climates for Impact Studies) to a semi-distributed soil moisture balance model (SMBM) in order to quantify the impacts of climate change on groundwater recharge and runoff in a medium-sized catchment (2098 km2) in the humid tropics of southwestern Uganda. The SMBM explicitly accounts for changes in soil moisture, and partitions effective precipitation into groundwater recharge and runoff. Under the A2 emissions scenario (2070–2100), climate projections from PRECIS feature not only rises in catchment precipitation and modelled potential evapotranspiration by 14% and 53%, respectively, but also increases in rainfall intensity. We show that the common application of the historical rainfall distribution using delta factors to the SMBM grossly underestimates groundwater recharge (i.e. 55% decrease relative to the baseline period of 1961–1990). By transforming the rainfall distribution to account for changes in rainfall intensity, we project increases in recharge and runoff of 53% and 137%, respectively, relative to the baseline period.

Hydrological modelling and the sustainable development of the Hadejia-Nguru Wetlands, Nigeria

Abstract The Hadejia-Nguru Wetlands produce agricultural, fishing and fuelwood benefits of upto 1277 Naira ha−1 (N1 = US

Environmental influences on the qualitative and quantitative composition of phytoplankton and zooplankton in North African coastal lagoons

22, October 1994), over five times the productivity of formal irrigation schemes. The wetlands play a vital role in aquifer recharge. The key is the annual wet season flooding of over 2000 km2 in the 1960s and around 1500 km2 in the 1970s. A water balance model, utilizing monthly hydrological and meteorological data simulates flood extent and groundwater storage within the wetlands. The model was operated between 1964 and 1987 and was calibrated using observed flood extents ranging from 50 to 3265 km2. Subsequently elements were added for dams and irrigation schemes. Results indicate that full implementation of all the schemes constructed or planned would cause flooding to be less than 375 km2for 60% of the time and groundwater storage to fall by over 5500 106 m3. It is possible to define an operating regime for the basins hydraulic structures which could provide artificial floods and ...

Soil Pollution: Urban Brownfields

Within the framework of the international research project MELMARINA, seasonal dynamics of plankton communities in three North African coastal lagoons (Merja Zerga, Ghar El Melh, and Lake Manzala) were investigated. The sampling period extended from July 2003 to September 2004 with the aim of evaluating hydrological and other influences on the structure, composition and space-time development of these communities in each lagoon. Phytoplankton in Merja Zerga showed a quasi-permanent predominance of marine diatoms in the open sea station and in the marine inlet channel. Dinoflagellates were abundant in summer and early autumn in the marine inlet and extended into the central lagoon station. In Ghar El Melh, marine species (especially diatoms and dinoflagellates) dominated despite occasional winter inflows of freshwater. In Lake Manzala, freshwater species generally predominated and the planktonic communities were comparatively very diverse. Chlorophyceae contributed 39% of the total species recorded and diatoms and cyanophyceans were also common; the Dinophyceae, Euglenophyceae, Chrysophyceae and Cryptophyceae less so. Zooplankton communities in both Ghar El Melh and Merja Zerga were dominated by marine copepods. Rotifera, Copepoda, Ostracoda, and Cladocera were recorded in both lagoons as were meroplanktonic larvae of Polychaeta, Cirripedia, Mysidacea and Gastropoda and free living nematodes. Ghar El Melh was the more productive of these two lagoons with spring and early summer being the productive seasons. Zooplankton communities in Lake Manzala were generally dominated by rotifers and highest zooplankton abundances occurred in April (2003). Sampling stations near the marine inlets showed the highest diversity and the zooplankton communities showed considerable spatial variation within this large lagoon. The three lagoons represent very different water bodies contrasted strongly in terms of tidal effects and freshwater availability. Yet, there are some similarities in ecosystem structure. Space-time development of the plankton communities was similar especially in Merja Zerga and Ghar El Melh. Species abundances and specific diversities indicated that seasonal changes in salinity and nutrient concentrations were the main influential factors. Lake Manzala was the most productive lagoon and all the three sites supported toxic algal species. Relatively low plankton biomass in Merja Zerga and Ghar El Melh probably resulted from a combination of factors including highly episodic nutrient inputs, light suppression (by turbidity) and nutrient competition with benthic algae. Water quality variables were largely driven by the hydrological regime specific to each lagoon. Nutrient enrichment and, particularly for Lake Manzala, sea level rise threaten the sustainability of the planktonic ecosystems in all three lagoons.

Sustaining China's Water Resources

Chinas plans to tackle farmland pollution and improve food safety are to be welcomed (“China gets serious about its pollutant-laden soil,” C. Larson, News & Analysis, 28 March, p. [1415][1]). However, the country faces equally serious urban soil and water pollution. As a result of unparalleled

Hydrological characteristics of three North African coastal lagoons: insights from the MELMARINA project

Chinas water crisis is receiving worldwide attention (“Water sustainability for China and beyond,” J. Liu and W. Yang, Policy Forum, 10 August 2012, p. [649][1]). The need for coordinating multiple government agencies has been highlighted, but involvement at both the corporate and the

Hydrology and land use in a sahelian floodplain wetland

Hydrological and hydrodynamic characteristics are important controls in all wetlands including coastal lagoons. Enhanced understanding of lagoon functioning can be obtained through the acquisition and interpretation of hydrological, meteorological and related data. The MELMARINA Project investigated links between hydrological and ecological conditions within North African coastal lagoons. It employed three primary sites: Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. Hydrological, meteorological and related data were acquired for these lagoons. Data included precipitation, evaporation, wind speed and direction, freshwater discharges into the lagoons, tides beyond the lagoons in the open sea, lagoon bathymetry and time series of lagoon water levels/depths. Data were acquired from secondary sources (including online archives) and targeted field survey and monitoring programmes. Interpretation of these data provides insights into the hydrological functioning of the lagoons and contributed to the modelling requirements of MELMARINA. The functioning of Merja Zerga is dominated by the exchange of water between the Atlantic and the lagoon. Large, tidally induced oscillations in water level are responsible for the inundation of extensive inter-tidal mudflats whilst the rapid replacement of water by exchanges with the sea diminishes the influence of freshwater inflows and winter rainfall. The smaller Mediterranean tides reduce the magnitude of lagoon–sea exchanges and result in much smaller water level oscillations within Ghar El Melh. As a result, this lagoon lacks the inter-tidal environments found within the Moroccan site and hydrodynamic conditions are more likely influenced by wind set up. Although freshwater inflows to Ghar El Melh are smaller than those in Merja Zerga, their effects, coupled with heavy winter rainfall, can persist due to longer residence times of water within the lagoon. Freshwater inflows are central to the functioning of Lake Manzala. Large discharges of relatively freshwater are provided by major drains which cross the Nile Delta. These influence lake water levels and are responsible for the freshwater conditions within large parts of the lake. The small tidal range of the eastern Mediterranean, coupled with constricted connections with the sea, reduces the influence of lake–sea exchanges and tidally induced water level oscillations within Lake Manzala.

Shale-gas plans threaten China's water resources

Africa’s numerous floodplain wetlands provide a host of hydrologic, ecological, economic, and social benefits. They play a fundamental role in supporting significant human populations. In common with all wetlands, the hydrology of Africa’s floodplains is central to their functioning and in turn plays a key role in determining the benefits that they provide. The timing and extent of wet-season inundation are major influences upon the temporal and spatial distribution of floodplain resource use. Using results from intensive hydrologic surveys, supplemented by analyses of river flow data and flood extent maps, this paper delineates areas within the Hadejia-Nguru Wetlands of northeastern Nigeria according to their hydrologic characteristics. This delineation is used in combination with a land-use map derived from aerial and field surveys to examine the impacts of hydrology upon human activities and land use. The timing of different cultivation practices in the wetlands is shown to be in tune with the annual flood cycle. Rice is cultivated in inundated areas that are then planted with other crops after the floods recede. The intensity of fishing and cattle grazing also varies with the pattern of rising and falling water levels. The distribution of major land uses is strongly influenced by spatial variations in hydrologic characteristics. The location of rice cultivation and small-scale irrigation is determined by water availability in the wet and dry seasons, respectively. Extensive flood rice farms are found along the Jama’are River, which contributes over 70% of the river inflow to the wetlands. Within the hadejia River system, important flood rice areas are the Madachi Swamp and the Marma Channel. The primary area of small-scale irrigation is along the Burum Gana River in which small, but year-round, flows are maintained by return flows from upstream irrigation schemes. This area, which covers only 13% of the land-use map, contains 48% of the area of small-scale irrigation. Extensive inundation seems to act as a barrier to human activities in some areas and is responsible for the maintenance of natural vegetation within central parts of the wetlands. Modifications to the hydrologic characteristics of some parts of the wetlands resulting from drought and upstream irrigation schemes have required local communities to adapt, with varying degrees of success, their modes of floodplain resource use. Farmers along the Burum Gana have embraced small-scale irrigation, while those along the Keffin Hausa River, which has all but dried up, have had no option but to concentrate on rain-fed agriculture. The strong inter-connections between hydrology, land use, and human activites dictate that any further hydrologic modifications should not be undertaken without a full appreciation of their potential impacts.

Sediment distribution and accumulation in lagoons of the Southern Mediterranean Region (the MELMARINA Project) with special reference to environmental change and aquatic ecosystems

The impact of shale-gas development on American water quality has received wide attention (“Impact of shale gas development on regional water quality,” R. D. Vidic et al. , Review, 17 May, p. [826][1]), but potential impacts of Chinas accelerating shalegas exploration on the nations water