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Hydrologic connectivity refers to the processes and thresholds leading to water transport across a landscape. In dryland ecosystems, runoff production is mediated by the arrangement of vegetation and bare soil patches on hillslopes and the properties of ephemeral channels. In this study, we used runoff measurements at multiple scales in a small (4.67 ha) mixed shrubland catchment of the Chihuahuan Desert to identify controls on and thresholds of hillslope‐channel connectivity. By relating short‐ and long‐term hydrologic records, we also addressed whether observed changes in outlet discharge since 1977 were linked to modifications in hydrologic connectivity. Hillslope runoff production was controlled by the maximum rainfall intensity occurring in a 30‐min interval (I₃₀), with small‐to‐negligible effects of antecedent surface soil moisture, vegetation cover, or slope aspect. AnI₃₀threshold of nearly 10 mm/h activated runoff propagation from the shrubland hillslopes and through the main ephemeral channel, whereas anI₃₀threshold of about 16 mm/h was required for discharge from the catchment outlet. Since storms rarely exceedI₃₀, full hillslope‐channel connectivity occurs infrequently in the mixed shrubland, leading to <2% of the annual precipitation being converted into outlet discharge. Progressive decreases in outlet discharge since 1977 could not be explained by variations in precipitation metrics, includingI₃₀, or the process of woody plant encroachment. Instead, channel modifications from the buildup of sediment behind measurement flumes may have increased transmission losses and reduced outlet discharge. Thus, alterations in channel properties can play an important role in the long‐term (45‐year) variations of rainfall–runoff dynamics of small desert catchments.

According to the Intergovernmental Panel on Climate Change (IPCC), global temperatures have risen at an alarming pace since the early 20th century and this warming has been more pronounced since the 1970s. Temperature variations are significant because of their relation with thermal comfort and public health. In this study, we characterize the impacts of increasing maximum air temperatures in Sonora, Mexico. Heat days (HDs) and heat waves (HWs) were used as indicators to investigate historical trends in extreme heat. Furthermore, HDs were represented using a generalized linear regression model during the observed period (1966–2015) to generate future scenarios related to extreme heat and subsequently compared with six downscaled general circulation models (CNRM‐CM5, CSIRO Mk3.6.0, HadGEM2‐CC, HadGEM2‐ES, IPSL‐CM5A‐LR and IPSL‐CM5A‐MR) under low and high radiative scenarios (RCP4.5 and RCP8.5). Results of this work indicate that climate stations in Sonora have exhibited increases in the number of HDs and HWs in the historical record that can be associated to physical factors such as elevation, urban land cover and the percent of annual rainfall during the summer. Statistical and model‐based projections indicate that these trends will continue in the future up to 2060, with less moderate increases and high uncertainty noted for the difference scenarios of the downscaled models. These observed and projected trends in extreme heat are important for identifying adaptation strategies in the public and environmental health sectors in Sonora.