The monsoon from the southwest and the mountains in central north and east delineate different climatic zones in Sri Lanka. Rice is the most important crop of the country and is mainly planted in the southwest and central highlands. Maize requires less water and is mainly grown in the north and west. This monitoring period covers the sowing and growing season within the main season (Maha), both for rice and maize. According to the CropWatch monitoring results, crop condition was average for the whole period in general.
Influenced by monsoon and topography, the country experienced typical rainy season conditions during October and November, followed by cold and dry conditions during December and January. Precipitation, temperature and radiation all increased compared to 15YA (RAIN +3%, TEMP +0.2℃, RADPAR +9%). The fraction of cropped arable land (CALF) remained comparable to 5YA. BIOMSS was up 7% as compared to 15YA. As shown on the NDVI development graph, NDVI values were apparently below average in mid-October and early December, while they were close to the 5YA for other periods. During the period of abnormal NDVI values, RAIN was much larger than 15YA and consequently affected the crop conditions. In spite of this, agroclimatic and agronomic indicators reflected the favorable environmental condition for crop growth during the monitoring period. NDVI trends revealed a good prospect for crop production. The maximum VCI for the whole country was 0.99.
As shown by NDVI clusters map and profiles, spatial heterogeneity of crop condition was significant throughout the country’s cropland. 28.8% of cropland showed consistent above-zero NDVI departure values, including parts of provinces of North Western, NorthCentral, Southern, Uva and Eastern Sri Lanka. 64.4% of cropland experienced large negative NDVI departure values in mid-October and early December. The regions were Kurunegala, Anuradhapura, the area between Colombo and Galle, and other scattered areas along the western coast. The area between Nuwara-Eliya and Badulla showed below-zero NDVI departure values for the whole period, which accounted for 6.8% of cropland. The VCIx map exhibited high values for almost the whole country.
Regional analysis
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.
The Dry zone
In the Dry zone, the recorded RAIN (925mm) was 3% below average and amounted to over 7 mm per day, which was sufficient for the growth of maize. TEMP was 0.3°C above average with RADPAR up as well, by 10%; BIOMSS and CALF increased by 9% and 1% compared to average. NDVI followed a similar trend as the whole county. The VCIx for the zone was 0.99. Overall, crop condition was fair in general.
The Intermediate zone
The Intermediate zone went through the end of the rainy season with RAIN at 1408 mm, 7% above 15YA. More than 11mm precipitation per day could meet the need of water for rice and maize in this zone. TEMP was comparable to average while RADPAR was up 8% above average. With full use of cropland, BIOMSS was close to the average (+1%). The variation of NDVI was analogous to the Dry zone. The VCIx value for the zone was 1. Condition of crop was assessed as average.
The Wet zone
The Wet zone received the most RAIN (1783mm) that was 7% up compared to 15YA. TEMP (+0.3°C) and RADPAR (+5%) were higher too. Favorable agroclimatic indicators led to a 7% rise in BIOMSS and cropland was fully utilized. NDVI was average for the whole period except for mid-October. The VCIx value for the zone was 0.99. Crop conditions were normal for this zone, and thus similar to the other two sub-national regions.
Figure 3.21. Sri Lanka crop condition, October 2019 - January 2020
(a) Phenology of major crops
(b) Crop condition development graph based on NDVI
(c) Rainfall profile
(d) Temperature profile
(e) Maximum VCI
(f) Spatial NDVI patterns compared to 5YA (g) NDVI profiles
(h) Crop condition development graph based on NDVI (Dry zone (left) and Wet zone (right))
(i) Crop condition development graph based on NDVI (Intermediate zone)
Table 3.50. Sri Lanka agroclimatic indicators by sub-national regions, current season's values and departure from15YA, October 2019 - January 2020
Region | RAIN | TEMP | RADPAR | |||
Current (mm) | Departure from 15YA (%) | Current (°C) | Departure from 15YA (°C) | Current (MJ/m2) | Departure from 15YA (%) | |
Dry zone | 925 | -3 | 25.4 | 0.3 | 1219 | 10 |
Wet zone | 1783 | 7 | 23.9 | 0.3 | 1074 | 5 |
Intermediate zone | 1408 | 6 | 23.3 | 0.0 | 1092 | 8 |
Table 3.51. Sri Lanka agronomic indicators by sub-national regions, current season's values and departure from 5YA, October 2019 - January 2020
Region | BIOMSS | CALF | Maximum VCI | ||
Current (gDM/m2) | Departure from 15YA (%) | Current (%) | Departure from 5YA (%) | Current | |
Dry zone | 818 | 9 | 100 | 1 | 0.99 |
Wet zone | 694 | 7 | 100 | 0 | 0.99 |
Intermediate zone | 686 | 1 | 100 | 0 | 1.00 |