Observed Trends and Variability in Climate Indices Relevant for Crop Yields in Southeast Asia

Climate indices are analyzed using a newly developed dataset with station-based daily data for Southeast Asia. With rice the staple food of the diet in the region, the indices used are aimed at agriculture, specifically rice production, and include the onset of the wet season and the nighttime temperature. Three indices are used to estimate the onset of the wet season. Despite a quantitative lack of similarity between these indices (although they are strongly correlated), the progression of the wet season over the area matches existing descriptions. Trends in the onset date of the wet season calculated over 1971-2012 are only statistically significant for a few stations; there are no signs that a wide spread delay as anticipated by future climate scenarios is already taking place. A positive trend in the nighttime temperature over the region is observed with values up to 0.7 degrees C decade(-1). For a selection of stations the change in distribution of nighttime temperatures is analyzed when comparing the 1971-90 period with the 1991-2010 period. They show a shift of the median to higher temperatures, and the decline in the number of relatively cool nights is stronger than the increase in the number of relatively warm nights.