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Highlights • Differences exist between the performances of various drought indices used to identify drought impacts on crop yields. • Multiscalar drought indices outperform uniscalar drought indices for monitoring the impact of drought on crop yields. • Shorter drought time-scales are better at identifying drought impacts on crop yields. Abstract This article presents an analysis of the response of the annual crop yield in five main dryland cultivations in the United States to different time-scales of drought, and explores the environmental and climatic characteristics that determine the response. For this purpose we analysed barley, winter wheat, soybean, corn and cotton. Drought was quantified by means of the Standardized Precipitation Evapotranspiration Index (SPEI). The results demonstrate a strong response in the interannual variability of crop yields to the drought time-scales in the different cultivations. Moreover, the response is highly spatially variable. Crop types showed considerable differences in the month in which their yields are most strongly linked to drought conditions. Some crops (e.g. winter wheat) responded to drought at medium to long SPEI time-scales, while other crops (e.g. soybean and corn) responded to short or long drought time-scales. The study confirms that the differences in the patterns of crop yield response to drought time-scales are mostly controlled by average climate conditions, in general, and water availability (precipitation), in particular. Generally, we found that there is a weaker link between crop yield and drought severity in humid environments and also that the response tends to occur over longer time-scales. [ABSTRACT FROM AUTHOR]

Highlights • Climate droughts control hydrological drought severity. • Hydrological droughts are complex and non-stationary. • In the U.S. there are very different patterns of hydrological drought responses. • Natural basins are characterized by different environmental conditions. Abstract We analyzed the relationships between meteorological drought and hydrological drought using very dense and diverse network of gauged natural drainage basins across the conterminous U.S. Specifically, this work utilized a dataset of 289 gauging stations, covering the period 1940–2013. Drainage basins were obtained for each gauging station using a digital terrain model. In addition to meteorological data (e.g., precipitation, air temperature and the atmospheric evaporative demand), we obtained a number of topographic, soil and remote sensing variables for each defined drainage basin. A hydrological drought index (the Standardized Streamflow Index; SSI) was computed for each basin and linked to the Standardized Precipitation Evapotranspiration Index (SPEI), which was used as a metric of climatic drought severity. The relationships between different SPEI time-scales and their corresponding SSI were assessed by means of a Pearson correlation coefficient. Also, the general patterns of response of hydrological droughts to climatic droughts were identified using a principal component analysis. Overall, results demonstrate a positive response of SSI to SPEI at shorter time-scales, with strong seasonality and clear spatial differences. We also assessed the role of some climatic and environmental factors in explaining these different responses using a predictive discriminant analysis. Results indicate that elevation and vegetation coverage are the main drivers of the diverse response of SSI to SPEI time-scales. Similar analyses were made for three sub-periods (1940–1964, 1965–1989 and 1989–2013), whose results confirm considerable differences in the response of SSI to SPEI over the past eighty years. [ABSTRACT FROM AUTHOR]