THAILAND:  Deficient Irrigation Supplies Reduce Dry Season Rice Production

Thailand’s 2012/13 second rice crop is currently suffering from an unusual problem – insufficient irrigation supplies. This high-yielding crop is typically cultivated in the winter dry season, with water supplied from large-scale reservoirs in upland mountain areas. Official in-country reports from USDA staff indicate that key reservoirs throughout the country are currently at record-low levels and that the Royal Irrigation Department (RID) has warned farmers it may not have sufficient supply to support late-planted rice. Satellite-derived vegetation index data, however, indicate that the majority of prime dry-season rice growing areas are already experiencing drought-like conditions, with well-below normal vegetative development in the middle of the growing season. The satellite-derived vegetation index uses the normalized difference vegetation index (NDVI) from NASA's MODIS Aqua satellite. The anomaly map, as displayed in the figure, is calculated using this year's data compared to the average values during the last 10 years. Typically, major crop regions anywhere in the world that display this level of negative NDVI anomalies subsequently experience reduced crop yield potential. Given the official government announcement of the critically short irrigation supply for the rest of the season, it is unlikely that crop conditions will sufficiently improve during the next 4-6 weeks to prevent widespread yield losses. On average, dry-season rice accounts for roughly 29 percent of total rice production.  In March 2013 USDA estimated Thailand’s total 2012/13 rice production at 20.5 million tons (milled basis), virtually unchanged from the previous year when record flooding devastated the Central Plains.

The record-low irrigation supplies which are negatively affecting 2012/13 dry-season rice production are a direct result of new government reservoir management policies following unprecedented flooding in central Thailand during the summer of 2011 - when over 1.3 million hectares of rice lands were inundated and roughly 1.0 million tons of milled rice production was lost. The 2011 floods were significantly exacerbated by massive emergency reservoir discharges that coincided with peak flood stages on the major tributaries of the Chao Phraya River in central Thailand. These discharges occurred when key mountain reservoirs filled past their structural capacity during heavy monsoon rains. The new reservoir management policy dictated that the majority of the country’s reservoir supplies would be discharged to the sea prior to the onset of the summer rainy season to prevent a repeat of the circumstances in 2011. Therefore, most surplus water supply in the country was drained from reservoirs in April 2012. Unfortunately, the plan failed to anticipate the possibility of a deficient monsoon, nor the consequences of having insufficient reservoir recharge prior to the onset of dry season rice cultivation. The 2012 monsoon subsequently provided minimal recharge of Thailand’s major reservoirs, and left total irrigation supply at record-low levels for the current dry-season crop.

USDA’s Foreign Agricultural Service (FAS) staff in Bangkok report that the majority of the 2012/13 dry-season rice crop was planted in a timely manner during the normal December-February period, with roughly 60 percent being sown by the end of January. As of mid-March it is estimated that approximately 20-30 percent of the total crop has been harvested, with the remaining 70-80 percent to be reaped between April-June. The heaviest period for harvesting activities is normally between April-May. The government has reported that roughly 48 percent of total dry season rice area, or 1.0 million hectares, is currently experiencing drought (insufficient water availability).

Dry-season rice production in Thailand, as in the remainder of Southeast Asia, is heavily dependent on irrigation. Approximately 70 percent of total dry-season rice area is fully irrigated, with the remainder relying on light-to-moderate winter rainfall. The non-irrigated portion of the dry-season crop is cultivated primarily in northern and northeastern provinces, and is interspersed with irrigated crops. Total dry-season rice area in the past few years has averaged about 2.0 million hectares, while crop yields average close to 4.3 tons per hectare (73 percent higher than those achieved in the summer wet season). Total national rice area, combining both wet and dry seasons, has averaged about 8.8 million hectares – meaning dry-season acreage accounts for roughly 23 percent of the total. The most important producing areas for dry-season rice (see map below) are in the wide alluvial flood plains of the Chao Phraya River, encompassing provinces in the lower North and Central Plains regions. These core areas alone account for roughly 65 percent of total dry-season rice production.

These normally high-producing rice areas are the same ones which satellite imagery currently indicates well-below normal growth and development have occurred through the first half of the 2012/13 growing season. Current crop conditions in the fertile “Central Plains” region north of the capital Bangkok (see image below) are a good example of the wider problem. These same rice growing areas typically show near-to-above normal vegetative development in mid-March (light to dark green in color). However this year, virtually all fields are reflecting a distinct reduction in crop development (orange to red color) compared to the long-term norm (10 years of comparative data). This satellite data generally indicates that the water shortage has been widespread through most of the major producing areas, and that overall crop development and yield potential on any unharvested lands is currently below average.

Current USDA area and production estimates for grains and other agricultural commodities are available on IPAD's Agricultural Production page or at PSD Online.