Future Climate Projection and Zoning of Extreme Temperature Indices

Global warming due to increasing carbon dioxide emissions over the past two centuries has had numerous climatic consequences. The change in the behavior and characteristics of extreme weather events such as temperature and precipitation is one of the consequences that have been of interest to researchers worldwide. In this study, the trend of 3 extreme indices of temperature: SU35, TR20, and DTR over two future periods have been studied using downscaled output of 3 GCMs in Razavi Khorasan province, Iran. The results show that the range of temperature diurnal variation (DTR) at three stations of Mashhad, Torbat-e-Heydarieh and Sabzevar during the base period has been reduced significantly. The trend of the number of summer days with temperatures above 35°C (SU35) in both Mashhad and Sabzevar stations was positive and no significant trend was found at Torbat-e-Heydarieh station. The number of tropical nights index (TR20) also showed a positive and significant increase in the three stations under study. The results showed highly significant changes in temperature extremes. The percentage of changes in SU35 index related to base period (1961–2014) for all three models (CNCM3, HadCM3 and NCCCSM) under A1B and A2 scenarios indicated a significant increase for the future periods of 2011–2030 and 2046–2065. TR20 is also expected to increase significantly during the two future periods. The percentage of changes of DTR into the future is negligible.

Challenges in constructing a high-resolution, multi-site, and multivariate weather generator and potential solutions

<p>A reliable simulation of the spatiotemporal characteristics of the meteorological field is of great significance for hydrological impact studies. To approach this target, a number of weather generators (WGs) have been developed over the past few decades. However, a detailed literature review shows that currently developed WGs are subject to one or several aspects of the following limitations: (1) low spatial and temporal resolutions to describe the real spatiotemporal dynamics of meteorological processes; 2) incapability to simulate a spatially coherent, temporally consistent, and physically meaningful meteorological field; and 3) inability to extend into the future in a climate change context. To tackle these problems, this study proposes some potential solutions: (1) using the multi-site multivariate WGs (MMWGs) to simulate the spatial, temporal, and inter-variable dependencies in the meteorological field; (2) coupling the MMWGs with the resampling-based algorithms to generate high-resolution spatiotemporal meteorological data; and (3) perturbing the parameters of the distribution and dependency models based on the future climate projection. A case study is carried out and shows that the proposed solutions are effective in addressing the aforementioned challenges. These findings could assist in developing high-resolution MMWGs for weather simulation and impact assessment.</p>

Response of Ice and Liquid Water Paths of Tropical Cyclones to Global Warming Simulated by a Global Nonhydrostatic Model with Explicit Cloud Microphysics

Cloud feedback plays a key role in the future climate projection. Using global nonhydrostatic model (GNHM) simulation data for a present-day [control (CTL)] and a warmer [global warming (GW)] experiment, the authors estimate the contribution of tropical cyclones (TCs) to ice water paths (IWP) and liquid water paths (LWP) associated with TCs and their changes between CTL and GW experiments. They use GNHM with a 14-km horizontal mesh for explicitly calculating cloud microphysics without cumulus parameterization. This dataset shows that the cyclogenesis under GW conditions reduces to approximately 70% of that under CTL conditions, as shown in a previous study, and the tropical averaged IWP (LWP) is reduced by approximately 2.76% (0.86%). Horizontal distributions of IWP and LWP changes seem to be closely related to TC track changes. To isolate the contributions of IWP/LWP associated with TCs, the authors first examine the radial distributions of IWP/LWP from the TC center at their mature stages and find that they generally increase for more intense TCs. As the intense TC in GW increases, the IWP and LWP around the TC center in GW becomes larger than that in CTL. The authors next define the TC area as the region within 500 km from the TC center at its mature stages. They find that the TC’s contribution to the total tropical IWP (LWP) is 4.93% (3.00%) in CTL and 5.84% (3.69%) in GW. Although this indicates that the TC’s contributions to the tropical IWP/LWP are small, IWP/LWP changes in each basin behave in a manner similar to those of the cyclogenesis and track changes under GW.