Robust late twenty-first century shift in the regional monsoons in RegCM-CORDEX simulations

AbstractWe use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas (GHG) forcing. All regional simulations are conducted using RegCM4 at a 25 km horizontal grid spacing using lateral and lower boundary forcing from three General Circulation Models (GCMs), which are part of the fifth phase of the Coupled Model Inter-comparison Project (CMIP5). Each simulation covers the period from 1970 through 2100 under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Regional climate simulations exhibit high fidelity in capturing key characteristics of precipitation and atmospheric dynamics across monsoon regions in the historical period. In the future period, regional monsoons exhibit a spatially robust delay in the monsoon onset, an increase in seasonality, and a reduction in the rainy season length at higher levels of radiative forcing. All regions with substantial delays in the monsoon onset exhibit a decrease in pre-monsoon precipitation, indicating a strong connection between pre-monsoon drying and a shift in the monsoon onset. The weakening of latent heat driven atmospheric warming during the pre-monsoon period delays the overturning of atmospheric subsidence in the monsoon regions, which defers their transitioning into deep convective states. Monsoon changes under the RCP2.6 scenario are mostly within the baseline variability

Quantifying the Relative Roles of Land Use Change and Remote Forcing on the 1930s Dust Bowl Drought

The 1930s Dust-Bowl drought in the U.S. Great Plains had devastating environmental and societal impacts. Understanding the causes of this persistent severe drought can help us to predict similar droughts and mitigate their effects. In this work, the Weather Research and Forecasting (WRF3.6) model, coupled with the Community Land Model (CLM4.0), was used to examine how land-cover change during the 1930s affected regional atmospheric circulation and resulted in a severe drought, and how this effect persisted in three different large-scale circulation (remote-forcing) conditions. Model simulation results show considerable decrease of the net surface radiation and subsequent reduction in the atmospheric radiation when using the 1930s land cover, compared to using the pre-settlement and present-day land cover. A compensating subsidence (warming) in the atmosphere causes an increase in pressure in the lower troposphere and near the surface. In the meantime, this process competes with the reduction of pressure stemming from a decrease in evaporative cooling. During the Dust Bowl, the changes in pressure in the U.S. Great Plains weakened the zonal pressure gradient force (PGF) over the Great Plains. Weakened PGF results in the collapse of the Great Plains low-level jet via the Coriolis’ effect and thereby reduces the transport of moisture to the Great Plains from the Gulf of Mexico. This reduction in moisture transport results in a decrease of 0.9mm/day of precipitation in the Great Plains, intensifying and sustaining the drought. Similar results have also been found in simulations using various large-scale circulations. They show the important role regional-scale land-cover change plays in sensitive areas of the development of severe drought relative to remote forcing

Índices de cambio climático y análisis de variabilidad en el estado de Veracruz, México

Ponencia presentada en: VII Congreso de la Asociación Española de Climatología: clima, ciudad y ecosistemas, celebrado en Madrid entre el 24 y 26 de noviembre de 2010.[ES]Se presenta un análisis de la señal del cambio climático y la variabilidad climática en el estado de Veracruz, México. El estudio de variabilidad natural se centra en detectar las variaciones de la precipitación debidas a teleconexiones con oscilaciones atmosféricas, como El Niño-Oscilación del Sur, (ENSO) Oscilación Decadal del Pacífico (PDO), Oscilación del Ártico (AO) y la Oscilación del Atlántico Norte (NAO). Para detectar la señal del cambio climático se utilizaron los índices del Grupo de Expertos en Detección e Índices de Cambio Climático (ETCCDI). Los resultados muestran evidencia de condiciones más cálidas en años recientes, aumento en la frecuencia de días calurosos y disminución de los días frescos. En la precipitación no se perciben cambios significativos en los registros anuales o en la ocurrencia de episodios extremos, sin embargo, en la mayor parte del estado la lluvia tiende a concentrarse en un menor período.[EN]An analysis on climate variability and change over the state of Veracruz, Mexico is presented. The study of natural variability is focused on detecting relationship with atmospheric oscillations. Thus, for this purpose, we analyze El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO) and North Atlantic Oscillation (NAO), finding almost no significant relationship. Regional climate change signals were evaluated using the methodology proposed by the Expert Team on Climate Change Detection and Indices (ETCCDI). The results show evidence pointing to warmer conditions in recent years, with an increased frequency of hot days and a decrease on cool days. For precipitation extreme indices no significant changes where estimated on annual basis, although a tendency to temporal concentration of rainfall was found.El financiamiento fue otorgado por el Programa Universitario de Cambio Climático de la Universidad Veracruzana y con becas del Consejo Nacional de Ciencia y Tecnología y la Secretaría de Educación Pública (México)

Predictability of the early summer surface air temperature over Western South Asia

Variability of the Surface Air Temperature (SAT) over the Western South Asia (WSA) region leads to frequent heatwaves during the early summer (May-June) season. The present study uses the European Centre for Medium-Range Weather Forecast’s fifth-generation seasonal prediction system, SEAS5, from 1981–2022 based on April initial conditions (1-month lead) to assess the SAT predictability during early summer season. The goal is to evaluate the SEAS5’s ability to predict the El Niño-Southern Oscillation (ENSO) related interannual variability and predictability of the SAT over WSA, which is mediated through upper-level (200-hPa) geopotential height anomalies. This teleconnection leads to anomalously warm surface conditions over the region during the negative ENSO phase, as observed in the reanalysis and SEAS5. We evaluate SEAS5 prediction skill against two observations and three reanalyses datasets. The SEAS5 SAT prediction skill is higher with high spatial resolution observations and reanalysis datasets compared to the ones with low-resolution. Overall, SEAS5 shows reasonable skill in predicting SAT and its variability over the WSA region. Moreover, the predictability of SAT during La Niña is comparable to El Niño years over the WSA region