Analysis of extreme rainfall trend and mapping of the Wadi pluvial flood in the Gaza coastal plain of Palestine

Abstract

In the eastern Mediterranean region of the Middle East and North Africa, pluvial flooding has become a common and severe climate change consequence event that requires immediate attention. The Wadi-Gaza basin is a critical source of surface water in Palestine; nevertheless, climate change and anthropogenic processes are altering the basin’s hydrological features, resulting in a series of extreme and disastrous flooding events in the coastal plain at the basin downstream. The Mann–Kendall test, Sen’s slope estimator, and the IPTA method that was used to analyze historical rainfall in the basin from 1979 to 2013 refer to a declining trend pattern, which reduces the surge of runoff discharge. Moreover, the future projection for the total monthly rainfall under the ensemble model of CIMP5 for the RCP scenarios of 2.60, 4.50, and 8.50 demonstrate a general decreasing trend in the rainfall with a variation ranging between about − 36 and − 53%. The frequency analysis for the maximum daily rainfall using different computing approaches shows that the theoretical maximum rainfall values for the assessment of flooding events were assigned to 22, 31, 35, 45 52, 59, 66, and 77 mm for the whole basin for the return periods (T) of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. The land cover–land use of the basin shows that 51% is barren land while the other portion is divided between urban (~ 16%), agricultural (~ 13%), and natural (~ 20%) lands. However, the type of soil that covers the basin is classified mainly as clay, loam, and sandy clay. According to the hydraulic analysis of downstream flooding, the volume of surge water that might reach the coastal plain in the event of water storms of 22 and 77 mm is around 6 and 118 million cubic meters, respectively. The area at risk of inundation due to floods in the Wadi-Gaza is between 3 and 17 km2, covering around 5–29 percent of the Gaza Strip’s middle governorate area, respectively.