Analysis of the observed trends in daily extreme precipitation indices in Gaza Strip during 1974–2016

There is a high-risk attendant on the changes in precipitation in developing countries, for example, Gaza Strip (GS). These changes have far-reaching social and economic ramifications by causing devastating flash floods and droughts. Based on the daily precipitation observations of eight meteorological stations over GS, from 1974 to 2016, the trends of 11 extreme precipitation indices (EPIs) were estimated using linear least squares method and then assessed statistically by Mann-Kendall test. The results show that, on average, most of the indices exhibited increasing trends during 1974–2016. It includes total wet-day precipitation (PRCPTOT), simple daily intensity index (SDII), and max 1-day precipitation (RX1day). Others were the max 5-day precipitation (RX5day), very wet day precipitation (R95p), extremely wet day precipitation (R99p), number of heavy precipitation days (R10mm), number of very heavy precipitation days (R20mm), and the number of consecutive dry days (CDD). Three of these indices passed the significance test (with p <.05): RX1day, RX5day, and R95p. Other EPIs, including number of wet days (R1mm) and consecutive wet days (CWD), exhibited non-significant decreasing trends. Spatially, many stations over GS exhibited opposite trends, especially in R1mm and CDD; however, they are separated by a few kilometres. Moreover, all EPIs have significant positive correlations with PRCPTOT at the 99% confidence level, except CDD (trend was non-significant). The contribution of extreme precipitation to annual PRCPTOT exhibited an increasing trend, which was significant at 62% of GS stations. The study indicates a potential increase in summer (drought) season.