Stochastic weather simulation, or weather generators (WGs), have gained a wide acceptance and been used for a variety of purposes, including climate change studies and the evaluation of climate variability and uncertainty effects. The two major challenges in WGs are improving the estimation of interannual variability and reducing overdispersion in the synthetic series of simulated weather. The objective of this work is to develop a WG model of daily rainfall, incorporating a covariable that accounts for interannual variability, and apply it in three climate regions (arid, Mediterranean, and temperate) of Chile. Precipitation occurrence was modeled using a two-stage, first-order Markov chain, whose parameters are fitted with a generalized lineal model (GLM) using a logistic function. This function considers monthly values of the observed Sea Surface Temperature Anomalies of the Region 3.4 of El Niño-Southern Oscillation (ENSO index) as a covariable. Precipitation intensity was simulated with a mixed exponential distribution, fitted using a maximum likelihood approach. The stochastic simulation shows that the application of the approach to Mediterranean and arid climates largely eliminates the overdispersion problem, resulting in a much improved interannual variability in the simulated values.

The near-surface temperature in Mediterranean climate-type regions has increased overall similarly or more rapidly than the global mean rates. Although these regions have comparable climate characteristics and are located at similar latitudes, recent warming acceleration is most pronounced in the Mediterranean Basin. Here, we investigate the contributions of several climate drivers to regional warming anomalies. We consider greenhouse gases, aerosols, solar irradiance, land–atmosphere interactions, and natural climate variability modes. Our results highlight the dominant role of anthropogenic greenhouse gas radiative forcing in all Mediterranean climate-type regions, particularly those in the northern hemisphere. In the Mediterranean Basin, the recent warming acceleration is largely due to the combined effect of declining aerosols and a negative trend in near-surface soil moisture. While land-atmosphere feedbacks are also important in other locations (e.g., California and Southern Africa), this synergy is unique in the Mediterranean Basin. These two regional climate drivers have natural and anthropogenic components of equivalent importance. Such feedbacks are not fully resolved in the current regional climate projections.

Extreme weather conditions, including intense heat stress due to higher temperatures, could trigger an increase in mortality risk. One way to evaluate the increase in mortality risk due to higher temperatures is the high risk warming (HRW) index, which evaluates the difference between the future and base period of a given percentile of daily maximum temperature (Tmax). Another is to calculate the future increase in the number of days over the temperature of such percentile, named high risk days (HRD) index. Previous studies point to the 84th percentile as the optimum temperature. Thus, this study aims to evaluate HRW and HRD indexes in Ecuador from 2011 to 2070 over the three natural climate zones, e.g., Coast, Andes, and Amazon. This climate analysis is based on historical data from meteorological stations and projections from CSIRO-MK36, GISS-E2, and IPSL-CM5A-MR, CMIP5 global climate models with dynamical scale reduction through weather research forecasting (WRF). The representative concentration pathways (RCPs), 8.5, were considered, which are related to the highest increases in future temperature. The results indicate that HRW and HRD will experience a larger increase in the period 2041–2070 compared with the period 1980–2005; in particular, these two indices will have a progressively increasing trend from 2011 onward. Specifically, the HRW calculated from the CMIP5 models for all stations is expected to grow from 0.6°C to 1.4°C and 1.8°C to 4.6°C for 2010–2040 and 2041–2070, respectively. Also, it is expected that the HRD for all stations will increase from 42 to 74 and 120 to 227 warming days for 2011–2040 and 2041–2070, respectively. The trends derived using Sen’s slope test show an increase in the HRW between 0.5°C and 0.9°C/decade and of the HRD between 2.88 and 4.9 days/decade since 1985. These results imply a high increase in heat-related mortality risks related to climate change in Ecuador. In terms of spatial distribution, three Ecuadorian regions experienced more critical temperature conditions with higher values of HRW and HRD for 2070. As a response to the increased frequency trends of warming periods in tropical areas, urgent measures should be taken to review public policies and legislation to mitigate the impacts of heat as a risk for human health in Ecuador.

<p>Mediterranean climate-type regions are characterized by warm-to-hot dry summers and mild, wet winters (Csa and Csb categories in Köppen classification). These regions are especially vulnerable to climate change since temperature and precipitation are expected to change in opposite directions. Impacts of extreme events (e.g., severe heat waves and prolonged droughts), challenges in water availability and food security, as well as other aspects of human livelihood, require a detailed global view of future changes in these unique mid-latitude zones.</p> <p>Here, we explore the observed trends and future distribution of global Mediterranean climate-type regions (MCR). We analyze gridded observations and a bias-adjusted and statistically downscaled dataset of five global Earth System Models from Coupled Model Intercomparison Project phase 6 (CMIP6). For supporting decision-making and climate mitigation efforts, we focus on different global warming levels (e.g., 1.5, 2, 3, and 4°C) derived from the Shared Socioeconomic Pathway SSP5-8.5.</p> <p>Our preliminary results show that for the rest of the 21st century, the CMIP6 models project that the total MCR area will not change significantly. However, our analysis highlights a robust poleward and eastward expansion of Csa zones at the expense of cooler climates (incl. Csb) over three regions, corresponding to a 21% increase in their area in the Mediterranean Basin, a 41% increase in North America-California, and 12.2% increase in South America-Central Chile. For every one additional degree of global warming, mean rainfall will likely decrease by about 4-5 % in most of the Mediterranean Basin, Southern Africa, and Southern Australia, while in South America-Central Chile, this decrease is more pronounced (near 10%). On the contrary, for every degree of global warming, mean rainfall will likely increase by about 5% in North America-California.</p>