Abstract
This study investigated the effects of climate change on water resources in the Kingdom of Saudi Arabia (KSA) using observational data and climate models. Data from 1950 to 2013 were analysed and modelled to provide a comprehensive reference document on the status of climate change in KSA. Climate predictions up to 2050 and 2075 were performed using seven climatic models, and the Standardised Precipitation Index was used to assess droughts over the past 64 years to avoid uncertainty in the form of inadequate precipitation records. The central-northern region received moderate rainfall (70-100 mm/year), while the central, north-eastern and south-western regions received the highest mean annual rainfall, ranging from 150 to 300 mm/year. Over time, the climate has become hotter, and rainfall has decreased slightly each year. The north-western and south-eastern regions received the lowest mean annual rainfall (4-50 mm/year). In terms of rainfall seasonality [coefficient variation (CV)], the central-northern region and the coastal regions had moderate annual rainfall variability (27-83 %); the central-western region had high variability (89-100 %). The eastern regions and Al-Riyadh had the highest variability, with CV values exceeding 100 % due to anomalies in the amount of precipitation over the years. The projection models predicted a declining trend in the mean annual precipitation for most regions of KSA under all of the studied scenarios. Models also showed a slight increase in the mean annual precipitation around the coastline of the Red Sea and in the southern regions. The drought analysis revealed that the whole of KSA has experienced long and extreme droughts presenting an alarming risk as most of these are agricultural regions. The risk will become extremely dangerous if the declining trend in rainfall continues, causing increasingly severe droughts.