Abstract
Outgoing Longwave Radiation (OLR), recognized as one of the key parameters in Earth's energy balance, plays a decisive role in atmospheric and climatic dynamics. This research was conducted to analyze the spatial patterns of OLR within the Lake Urmia basin. To achieve this objective, daily OLR data with a spatial resolution of 0.25° × 0.25° for a 37-year period (1987–2024) were obtained from the NOAA database, along with daily climatic data from 12 synoptic stations. The research methodology was based on statistical analyses, including the calculation of seasonal and annual means, trend identification using non-parametric Mann-Kendall tests, and Analysis of Time-Lagged Correlation Fields. The results indicated that the spatial pattern of the annual mean OLR in the Lake Urmia basin is a function of climatic elements. Specifically, the minimum OLR values, approximately 220 W/m², were observed over the highlands, while the maximum values, exceeding 260 W/m², were recorded in the low-lying and desert regions of the eastern basin. Statistical trend analysis over the 37-year period revealed a significant increase in annual OLR, with an average rate of 0.1095 W/m², indicating an intensification of long-term warming processes. Furthermore, the changes in OLR within this basin showed a significant correlation with various climatic parameters, highlighting the high sensitivity of OLR to climatic changes and meteorological fluctuations in the Lake Urmia basin. Consequently, OLR can serve as an effective index for monitoring drought and land cover changes.