Temporal variability of temperature, precipitation, drought, and their potential influence on horizontal visibility over Saudi Arabia

Changes in the hydrological cycle alter the meteorological variables trend over time, leading to higher extreme events. In this study, the spatial and temporal variability of horizontal visibility (VIS), maximum temperature (Tmax), minimum temperature (Tmin), precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI) are assessed over Saudi Arabia for the study period (34 years, i.e., 1985-2018) and two subperiods (1985-2001 and 2002-2018). The temporal variability of the variables is investigated for five climatic regions, using the Sen's slope, Mann Kendall test, modified MK, and cumulative sum (CUSUM). Results confirm that precipitation over regions has declined by more than 21.1% during the second subperiod (2002-2016) compared to the first subperiod (1985-2001). Combined with the reduction in precipitation, a high increase in minimum temperatures in the second period contributes to the evolution of drought and visibility degradation. The onset of severe drought events (after the late 2000s) corresponds to an acceleration of VIS degradation. The change points for VIS occurred earlier in the arid regions (Northern and Interior regions, 2007 and 2008, respectively) and 2011-2012 for the rest. The change points for precipitation, Tmax, and SPEI series occurred in late 1990, while for Tmin, it occurred in 2010. In the first period, VIS show weak to moderate correlations with drought indices (12-month SPEI) for all regions, except for the Coastal region. In the second period, Northern, Interior, and Coastal regions show strong correlations between VIS and SPEI 12, while mountain regions (Highland and Southern) show moderate to week correlations between VIS and SPEI 12. The abrupt changes in climate teleconnection indices, which has a higher influence on Tmin in the second subperiod, may be the reason for drought evolution and visibility degradations.