Design rainfall in Qatar: sensitivity to climate change scenarios

Design rainfall is needed in the design of numerous engineering infrastructures such as urban drainage systems, bridges, railways, metro systems, highways and flood levees. Design rainfall is derived using regional frequency analysis approach based on observed rainfall data from a large number of stations within a homogeneous region. This paper provides an assessment of the possible impacts of climate change on design rainfalls in Qatar. The future climate conditions are established based on AR4 and A2 categories of emission scenarios (SRES) specified by the Intergovernmental Panel on Climate Change. Predicted 24-h annual maximum rainfall series for both the wet (NCAR-CCSM) and dry scenarios (CSIRO-MK3.5) for the Qatari grid points are extracted for three different periods, which are current (2000-2029), medium-term (2040-2069) and end-of-century climates (2080-2099). Using an L-moments-based index frequency approach, homogeneous regions are established and the best-fit distribution is then used to derive rainfall quantiles for average recurrence intervals (ARIs) of 2, 5, 10, 25, 50 and 100 years. The results show that there is no significant change in the design rainfalls in Qatar in the short term covering 2040-2069; however, a significant change is predicted at the end of century covering 2080-2099. Updated design rainfalls are estimated considering climate change scenarios for the period of 2080-2099 by averaging results from the wet and dry climate scenarios. The increase in 24-h annual maximum rainfall for the period 2080-2099 (compared with the current period 2000-2029) is found to be in the range of 68 and 76 % for 100-year ARI. For the typical design ARIs of 10-20 years, the increase in design rainfall is found to be in the range of 43 and 54 %. The method presented in this study can be applied to other arid regions, in particular to the Middle Eastern countries.