摘要：Extreme heat is an emerging threat to the agricultural sector, which severely affected the crop yieldsin many regions of Romania during the last two decades. Here we investigate a 53-year climatology of dailymaximum air temperatures to extract the regional characteristics of summer heat stress in the southern croppinglowlands of Romania (Oltenia and Muntenia regions) and to estimate the yield sensitivity of three major crops(winter wheat, grain maize and sunflower) to the changing heat stress under the ongoing warming. In ourapproach we aim to test the hypothesis of a cause-effect relationship between seasonal heat stress and the annual cropproduction at county level (NUTS3), considering the existing adaptation potential through irrigations, especiallyduring the heat stress representative years of 2000, 2007 and 2012. Our results reveal that, in both croppingregions, there is a significant and spatial robust increase in the frequency and duration of heat stress, especiallysince the mid-1980s, confirming the findings of previous studies on climate variability and climate extremes.The changes in summer heat stress determined different and spatially variable crop yield sensitivities. The mainfindings of the regression analyses on heat stress-crop yield relationships are: summer heat stress allowedexplaining 17 to 55% of the annual variability of yields at county level; during the hot and droughty summers of2000, 2007 and 2012, the detrimental effect of heat stress on crop yields was particularly evident and worsenedby the lack of efficient water compensations through irrigations (generally below 5% in Oltenia and 7% inMuntenia); heat stress was found to be an important predictor of crop yield failures, especially for maize crops;for the summer harvesting crops (winter wheat) and good high temperature and drought resistance (sunflower),the detrimental effects of heat stress appear less evident; recurrent heat stress days (HSD, HSDD) and heatstress spells (HSSfr) have had a greater influence on final crops than the persistent individual heat stress spells(HSSdurmax). Both agricultural regions are heat stress sensitive, but the cropping areas which underwentsubstantial crop production losses due to extreme high temperatures are located in the southernmost floodplainareas (e.g. in the Dolj, Olt, Gorj, Giurgiu, Călăraşi counties), where heat stress is particularly intense andfrequent. Rehabilitation of irrigation emerges as an important adaptation measure in agriculture to reduce thecurrent vulnerabilities and future impacts of heat stress on national food security.
关键词：heat stress;crop yield;summer warming;southern cropping regions of Romania
