This study evaluates the potential of gridded AgMERRA (the Modern-Era Retrospective Analysis for Research and Applications) to estimate aridity index (AI), growing degree days (GDD), and temperature seasonality (TS) for six land stations across northeast Iran. The researcher investigated the spatiotemporal variation of the AgMERRA-derived agro-climatic indices for the entire period 1981–2010 and three 10-year sub-periods for the 347 wheat harvested grid cells (0.25° × 0.25°) and their utility for agro-climate zoning in northeast Iran. Results indicated a good agreement between AgMERRA daily solar radiation, maximum and minimum temperatures, and annual total precipitation with corresponding land observations for the six studied sites. AgMERRA-derived evapotranspiration (ET_o), AI, GDD, and TS also exhibited good agreement (R² and d > 0.7) with the land station–derived indices for most of the locations. Annual analysis of the AI indicated a negative trend for all of the wheat harvested grid cells, but the decrease was significant (p < 0.05) only for 14.70% of grid cells, which were located in the southwest part of the studied region. The magnitude of the significant decreasing trends in annual AI was (−)0.0011 per year. The increase in aridity was due to the concurrent occurrences of positive ET_o trends and negative precipitation trends. All of the wheat harvested grid cells showed a significant increasing trend (p < 0.05) for GDD at the rate of 24.10 °C d year⁻¹. The TS series demonstrated an apparent increasing trend for 99.2% of wheat harvested grid cells; however, only 16.9% of them had the significant positive trend (p < 0.05) with the average rate of 0.023 °C year⁻¹. The wheat harvested grid cells with increasing trend for TS were mainly distributed in the arid mountainous southern part of the study area. The 10 years sub-periods revealed that the best conditions in terms of most of the studied agro-climatic indices were found in sub-period 1981–1990 and the north Khorasan had better conditions in all three sub-periods. Based on AI, GDD, and TS, 13 major gridded agro-climatic zones were recognized in northeast Iran.

本研究评估了网格化 AgMERRA（用于研究和应用的现代回顾分析）估计伊朗东北部六个陆地站的干旱指数 (AI)、生长度日 (GDD) 和温度季节性 (TS) 的潜力。研究人员调查了 1981-2010 年整个时期和 347 个小麦收获网格单元（0.25° × 0.25°）的三个 10 年子时期的 AgMERRA 农业气候指数的时空变化及其对农业的效用。伊朗东北部的气候分区。结果表明，AgMERRA 每日太阳辐射、最高和最低温度以及年总降水量与六个研究地点的相应陆地观测值之间存在良好的一致性。AgMERRA 衍生的蒸散量 (ET _o)、AI、GDD 和 TS 也与大多数位置的陆地站派生指数表现出良好的一致性（R ^{2和 d > 0.7）。}AI 的年度分析表明，所有小麦收获的网格单元都呈负趋势，但仅 14.70% 的网格单元下降显着（p < 0.05），这些网格单元位于研究区域的西南部。年度 AI 显着下降趋势的幅度为 (−)0.0011 每年。干旱的增加是由于同时出现正的ET _o趋势和负的降水趋势。所有小麦收获的网格单元都显示出GDD 以 24.10 °C d 年^{-1的速率显着增加的趋势 (} p < 0.05 ). TS 系列显示 99.2% 的小麦收获网格单元有明显的增加趋势；然而，其中只有 16.9% 有显着的正趋势（p < 0.05），平均增长率为 0.023 °C 年^-1。TS呈增加趋势的小麦收获网格单元主要分布在研究区南部干旱山区。10 年子时期表明，就大多数所研究的农业气候指数而言，最佳条件出现在 1981-1990 年子时期，而北呼罗珊在所有三个子时期都具有更好的条件。基于 AI、GDD 和 TS，在伊朗东北部识别出 13 个主要的网格化农业气候带。