El Niño-Southern Oscillation and rainfall characteristics in Northern Thailand: implications for adaptation in rainfed farms

Certain factors reduce crop yield in rainfed agriculture, which affects food security. An indicator for predicting these situations for crop pattern and water management would therefore be useful for rainfed agriculture. This study focuses on developing the relation between the El Niño-Southern Oscillation (ENSO) and rain characteristics for crop planning in rainfed agriculture using a case study in Nan Province, Thailand. We focused on dry conditions that cause insufficient water availability for crops. Weak, moderate, or severe El Niño event intensities did not have any impacts on the late rainy season start date, shorter growing season, reduced rainfall, or fewer rainy days. Only El Niño events with very strong intensities (VSE) were more likely to have an influence on dry conditions. Apart from VSE, the neutral phase of ENSO had a stronger influence on these dry conditions. The Standardized Precipitation Evapotranspiration Index (SPEI) was applied to differentiate years with neutral ENSO phases, which caused late rainy season start, shorter growing season length, reduced rainfall, and fewer rainy days compared with other neutral phase years. As a result, a neutral ENSO phase occurred if the SPEI levels in March, April, and May were at a high drought intensity. Considering the rainy season start, average growing season length, and reproductive growth stage of rice and maize, suitable planting dates were determined for five groups of ENSO phases, including (1) El Niño, (2) La Niña, (3) neutral, (4) very strong El Niño, and (5) neutral with extremely dry conditions.