Seasonal Day–Night thermal asymmetry and diurnal temperature range change in a climatically diverse arid region: Insights from per-pixel Theil–Sen and Mann–Kendall analysis of MODIS data (2003–2023)

Characterizing diurnal surface thermal contrasts remains difficult in climatically diverse arid regions, particularly at subnational scales where observations are scarce. Jazan, in southwestern Saudi Arabia, combines hyper-arid coastal plains, transitional foothills, and the western Sarawat escarpment within one administrative boundary. Seasonal daytime land surface temperature (LST), nighttime LST, and surface diurnal temperature range (DTR) were analyzed for its 17 governorates over 2003–2023 using MODIS Terra Collection 6 eight-day composites. Trends were estimated with the Theil–Sen slope and the Mann–Kendall test. Nighttime LST increased significantly in 49 of 68 governorate–season combinations, most strongly in summer (+1.58 °C decade -1 ). Significant daytime cooling occurred in 14 combinations, 11 of them in autumn, whereas summer daytime trends were positive but not significant. Autumn DTR declined significantly in all 17 governorates (−0.84 to −2.13 °C decade -1 ). Restricting the analysis to 2003–2020, to limit the effect of Terra orbital drift, did not change the direction of any significant trend. Autumn DTR decline remained significant in 14 governorates, while autumn daytime cooling mostly lost significance. At the pixel scale, the strongest trends occurred in the middle-to-upper part of the regional LST distribution, mainly across the foothills and inland plains. Nighttime warming remained field-significant after accounting for temporal autocorrelation and multiple comparisons. Nighttime anomalies shifted from negative to positive around 2014–2015, but change-point analyses indicated gradual warming rather than an abrupt shift. Overall, surface DTR contracted in Jazan, contrasting with the global DTR expansion reported since the 1990s.