The effects of climate change on water resources. The Distributed Catchment Scale Model, DiCaSM application in Cyprus, Italy, Brazil, and the United Kingdom

Chapter 2. This chapter will briefly describe some climate change impact studies carried out in some countries Cyprus Island, Italy, Brazil and the UK. These studies were carried out at catchment scale, all used the same model, the Distributed Catchment Scale Model, DiCaSM. The results of Cyprus’ two south catchments showed that by 2050, relative to baseline data, groundwater and surface water supplies would decrease by 35% and 24% for the Kouris and 20% and 17% for the Akrotiri catchments, respectively. The gap between water supply and demand showed a linear increase with time. The results of the model run for the Candelaro catchment in the south of Italy showed that by 2050 the groundwater recharge would decrease between -20% and -30% and stream flows would be reduced between -16% and -31%, relative to the baseline data. Plotting the future water supply against the projected future water demand, for the Candelaro catchment area, showed the gap between water demand and water supply (groundwater and surface water, decreasing up to 2050) would increase in all scenarios and on average by up to 15% over time. The results of Mimoso and Tapacurá catchments of the Brazilian semi-arid regions in the northeast of Brazil indicated that for the Mimoso catchment, under the average of dry high and dry low emission scenarios, a forecasted reduction by 35%, 68%, and 77%, in groundwater recharge, GWR, and by 34%, 65%, and 72% in streamflow, for the time spans 2010–2039, 2040–2069, and 2070–2099, respectively, is expected. On the other hand, the Tapacurá catchments results indicated the possibility of reduction by 13.90%, 22.63% and 32.91% in groundwater recharge and by 4.98%, 14.28% and 20.58% in surface flows for the time spans 2010–2039, 2040–2069, 2070–2099, respectively. The study on the impact of future climate change on the UK water resources, with particular interest in drought, was carried out on seven catchments from north to south and from west to east to represent the rainfall and temperature gradient across the whole UK. The results of three representative catchments (from south to middle to north) out of the seven catchments are reported in this chapter. The selected catchments are Eden in the north (Scotland), Don in the midlands, and Pang in southeast of the UK. The results of the modelling work for the Eden catchment indicated that the most significant reduction in stream flow is expected in the summer season under all emission scenarios, the summer streamflow is likely to decrease, by 9.6 to17.8% in the 2020s, by 14.9 to 21.34% in the 2050s and by up to 25.2% in the 2080s under high emission scenarios. The study also pointed out that the groundwater recharge is likely to be reduced in the future with the largest decrease in groundwater recharge expected in the second half of the century, as it may decrease by up to 20.26% under the high emission scenario in the 2080s during the summer months. Overall, groundwater recharge during the summer months is much less than other seasons. The results of the Don catchment indicated that the most significant reduction in stream flow is expected in the summer season. During the 2020s period, in summer, a significant decrease in stream flow is projected to decrease by 13 to15% while in the 2050s, a decrease is projected from 27 to 29% and during the summers of the 2080s, the stream flow is likely to decrease by 24 to 42%. The groundwater recharge projections suggest that groundwater recharge might decrease by 3.4 to 11.3% under all emission scenarios during the winter months (December, January and February). The highest decrease of over 40% in summer groundwater recharge projected for the 2080s. The results of the Pang catchment indicated that the stream flow decrease in the 2020s ranged from 11.7% to 21.6%, in 2050s from 19.0 to 36.7% and 2080s from 21.4 to 46.6% with the lower values associated with the low emission and higher values in the range associated with the high emission. The GWR decrease in the 2020s ranged from 16.9% to 41%, in 2050s from 28.0 to 62.3% and 2080s from 28.7 to 71.7% with the lower values associated with the low emission and higher values in the range associated with the high emission scenario. The drought indices such as Standardized Precipitation Index, adjusted Standardized Precipitation Index, SPEI, which takes ET into account, Reconnaissance Drought Index, RDI and the adjusted RDI which includes actual ET instead of potential ET and net/effective rainfall instead of total/gross rainfall, Soil Moisture Deficit, Wetness Index and River Water Depth were computed for future climate change scenarios for the UK catchments. The indices were able to accurately reproduce the past drought events. In addition, they predicted the future ET, SMD, WI, RDI/RDIE, SPI/SPEI, stream depth and the future number of drought events and their severity level. The results indicated future increases in the ET, SMD and decreases in WI, SPI/SPEI. The decrease or increase gets more significant with increasing the emission level from low to medium to high and with time from the 2020s to 2080s. In addition, the RDI/RDIE analysis indicated the possibility of increasing the number of drought events, their frequency of occurrence and severity levels will increase with increasing the emission level from low to medium to high and with time from the 2020s to 2080s. The gap between water supply and demand was calculated for the Cyprus’ two catchments Kouris and Akrotiri and for the Italian catchment, Candelaro, showed a widening up to 2050. Similarly, six out of the seven catchments of the UK (apart from Eden in Scotland) showed a similar widening gap between future water supply and future water demand and that gap is widening over time up to 2099 if water demand is not sustainably managed and controlled. New policies to mitigate and adapt to climate change are needed to cope with the impact of climate change in order to ensure water and food security for the 9.8 billion inhabitants by 2050.