This report covers the second season (Yala) growing and harvesting for rice and maize from July to September, as well as the main season (Maha) sowing for crops in October. According to the CropWatch monitoring results, crop conditions were near average for the period from July to October.
Similar to the last monitoring period, this period was dominated by the south-western monsoon, which is active between May and September. At the national level, temperature experienced a slight increase (TEMP +0.2℃), while precipitation and radiation decreased as compared to the 15YA (RAIN -23%, RADPAR -3%) . The decrease in rainfall mainly happened between August to October, which are harvesting and sowing periods. The fraction of cropped arable land (CALF) remained nearly comparable to the 5YA, while cropping intensity increased by 22% than the 5YA. BIOMSS was 3% down comparable to the 15YA. As shown on the NDVI development graph, NDVI values were near average from July to August and slightly below-average from September to October. The below-average NDVI values in September and October can be seen as a result from the significantly reduced precipitation. Nevertheless, the normal NDVI values in growing season indicated good condition for biomass accumulation and favorable prospect of crop production. The maximum VCI for the whole country was 0.95.
与上一个监测期类似，本监测期内来自西南方向的季风在5月至9月间盛行。在全国范围内，监测期内的平均气温较过去15年平均水平略有偏高（ + 0.2℃），而累计降水（-23％）和光合有效辐射（-3％）则均有所偏低，其中降水减少主要发生在8月至10月间的收获期和播种期。耕地种植比例几乎与近5年平均水平相当，而复种指数较近5年平均水平偏高22%，潜在生物量则较平均水平偏低3％。基于NDVI的作物生长过程线显示，NDVI值在7月至8月接近平均水平，而在9月至10月则略有偏低。其中后者所显示的偏低可以认为是降水显著减少所导致的。然而，NDVI值在生长期内处于平均水平，这表明作物生物量积累的状况较好，作物产量具有良好的前景。该国在监测期内的最佳植被状况指数为0.95。
As shown by the NDVI clusters map and profiles, the trends were quite different across the island. More than half of the country’s cropland showed below-zero NDVI departure values during the whole period. 10% of cropland showed a large decline of NDVI values in early August, as well as the 6.5% of cropland in early August and late September, which may have been outliers due to cloud cover. These croplands with negative NDVI departure values were mainly distributed in the north and southwest part of the country, including south of North Western Province, North Central Province, Western Province and Southern Province. Almost half of the cropland, i.e., 44.3%, showed above-zero NDVI departure values before mid-October. These croplands were distributed in North Western Province, Eastern Province and Uva Province.
Based on the cropping system, climatic zones and topographic conditions, three sub-national agroecological regions can be distinguished for Sri Lanka. They are the Dry zone, the Wet zone, and the Intermediate zone.
In the Dry zone, the recorded RAIN (361 mm) was 41% below average and amounted to more than 3 mm per day, which was close to the water demand of the growth of maize in this region. TEMP was 0.2°C above average with RADPAR down (-4%) and BIOMSS also decreased by 5% as compared to the 15YA. CALF was near the 5YA level and 97% of cropland was utilized. NDVI followed a similar trend as the whole county. The VCIx for the zone was 0.93. Overall, crop conditions were below-average for this zone.
The Wet zone received the highest precipitation among three sub-national regions. RAIN (1836 mm) was down by 13% as compared to the 15YA. TEMP and RADPAR were near average. BIOMSS was comparable to the 15YA and cropland was fully utilized as usual. NDVI values were below-average almost for the whole period, especially in from July to September. The VCIx value for the zone was 0.98. Crop conditions were also below-average for this zone.
The Intermediate zone also experienced deficient rain (RAIN 840 mm), 25% below the 15YA. This is 7 mm per day and is supposed to be sufficient for rice and maize. TEMP was average and RADPAR down by 2% compared to the 15YA. With full use of cropland, BIOMSS was 3% below average. Similar to the last report, the NDVI values fluctuated around the average and the VCIx value for this zone was 1. Conditions of crops were assessed as near average.
图 3.27 2020年7月-10月斯里兰卡作物长势
(f) NDVI距平空间聚类图（与5年平均相比） (g) NDVI距平聚类过程线
表 3.45 斯里兰卡农业生态分区2020年7月-10月与过去15年(15YA)同期农业气象指标
表 3.46 农业生态分区2020年7月-10月与近5年 (5Y)同期农情指标