Annual Cycle Of Precipitation Research Articles

Comparison of five gridded precipitation products at climatological scales over West Africa

The paper aimed at assessing the capabilities and limitations of five different precipitation products to describe rainfall over West Africa. Five gridded precipitation datasets of the Tropical Rainfall Measurement Mission (TRMM) Multi-Platform Analysis (TMPA 3B43v7); University of Delaware (UDEL version 3.01); Climatic Research Unit (CRU version 3.1); Global Precipitation Climatology Centre (GPCC version 7) and African Rainfall Climatology (ARC version 2) were compared and validated with reference ground observation data from 81 stations spanning a 19-year period, from January 1990 to December 2008. Spatial investigation of the precipitation datasets was performed, and their capability to replicate the inter-annual and intra-seasonal variability was also assessed. The ability of the products to capture the El Nino and La Nina events were also assessed. Results show that all the five datasets depicted similar spatial distribution of mean rainfall climatology, although differences exist in the total rainfall amount for each precipitation dataset. Further analysis shows that the three distinct phases of the mean annual cycle of the West Africa Monsoon precipitation were well captured by the datasets. However, CRU, GPCC and UDEL failed to capture the little dry season in the month of August while UDEL and GPCC underestimated rainfall amount in the Sahel region. Results of the inter-annual precipitation anomalies shows that ARC2 fail to capture about 46% of the observed variability while the other four datasets exhibits a greater performance (r > 0.9). All the precipitation dataset except ARC2 were consistent with the ground observation in capturing the dry and wet conditions associated with El Nino and La Nina events, respectively. ARC2 tends to overestimate the El Nino event and failed to capture the La Nina event in all the years considered. In general GPCC, CRU and TRMM were found to be the most outstanding datasets and can, therefore, be used for precipitation assessment over West Africa.

Seasonal and Spatial Variation of Surface Urban Heat Island Intensity in a Small Urban Agglomerate in Brazil

In recent years, SUHIs (surface urban heat islands) have been greatly emphasized in urban climate studies, since it is one of the climate phenomena most influenced by human action. In this study, temporal and spatial variations of SUHIs in the cities of Ceres and Rialma (Brazil) were investigated; satellite Landsat 8 TIRS/OLI images from 2013 to 2016 were used for this purpose. The results showed that in all seasons, two relationships were observed, one positive and one negative. An N D V I (Normalized Difference Vegetation Index) of 0.2 is the divider of this relationship: up to this value, the relationship is positive, that is, the higher the N D V I value, the higher the surface temperature, while the relationship is negative at an N D V I greater than 0.2. There was high seasonal variation in the SUHIs, with the highest intensities recorded in the spring and summer (±12 °C), and the lowest in the winter. These temporal variations were attributed to the annual cycle of precipitation, which directly involves the robustness of the Cerrado vegetation. SUHIs occupied, on average, an area three times larger than the area of SUCIs (surface urban cool islands). The highest values of SUCIs were observed in water bodies and in valley bottoms. Overall, SUHIs showed high intensities; however, a more intense core area, such as in large cities, was not observed.

Eventos de Precipitação Extrema na Região do Centro de Lançamento de Alcântara

Resumo Totais diários de precipitação foram utilizados para identificar os eventos de Precipitação Extrema (PE) na região do Centro de Lançamento de Alcântara (CLA) para o período de set-1984 a ago-2014 (30 anos). Adotando o 99° percentil dos totais diários (44 mm d-1) como limiar de PE, foram identificados 104 eventos no período. O ciclo anual da frequência de eventos e das excedências foi muito semelhante ao ciclo anual da precipitação, com máximo (mínimo) no trimestre MAM (SON). Utilizando as séries de duração parcial, os máximos anuais de total diário (definindo ano hidrológico como os 12 meses a partir de setembro) puderam ser modelados estatisticamente como uma distribuição de Gumbel. A precipitação de 1 dia com tempo de retorno de 100 anos seria de 115 mm, valor inferior aos encontrados na literatura para localidades pertencentes à região do CLA. Para o bimestre de março e abril, que concentrou a maior frequência de eventos, a variabilidade interanual da frequência esteve correlacionada positiva e significativamente (R = +0,44) com o total de precipitação, e a correlação parcial com outros fatores (índice Niño 3, gradiente inter-hemisférico de temperatura da superfície do mar do Atlântico e vento em 925 hPa sobre a região do CLA) não foi significativa. Os dias de PE no bimestre diferenciaram-se dos demais com totais elevados por apresentarem maior número de horas do dia com chuva (14 ± 4 h) e maiores totais horários (p. ex., total horário máximo = 23 ± 9 mm h-1). No bimestre de março e abril de 1996, quando houve a maior frequência de eventos (5 eventos), os dias de PE caracterizaram-se pela ocorrência de atividade convectiva intensa sobre duas grandes áreas: uma zonalmente alongada cobrindo a costa norte do Brasil, e outra cobrindo os Estados de Santa Catarina e Paraná.

Temporal patterns of precipitation and vegetation variability over Botswana during extreme dry and wet rainfall seasons

ABSTRACTThis study investigates the temporal evolution of extreme rainfall seasons over Botswana, and their relationships to the growing season cycle of natural vegetation. Ground‐based precipitation data and remotely sensed Advanced Very High Resolution Radiometer (AVHRR)‐normalized difference vegetation index (NDVI) data are analysed for the July 1981–June 2006 period. Results confirm that Botswana's annual cycle of precipitation is characterized by substantial intra‐seasonal variation, which is resonated in natural vegetation cover. During extreme wet (dry) years, the most extreme surpluses (shortfalls) of monthly rainfall were observed in the middle of the rainfall season (January–February). While rainfall receipts during season onset and cessation may not be the highest, they were found to have strong influence on NDVI coefficient of variation. Extreme wet seasons could be distinguished from moderate wet seasons by examining their monthly peak patterns. Furthermore, the November–December period was identified through the NDVI as the critical period when extreme conditions may begin to emerge. These findings could have important implications for supporting seasonal forecasts and optimizing rainfed agricultural adaptation and natural resources management in southern Africa.

Sensitivity analysis of different parameterization schemes using RegCM4.3 for the Carpathian region

In order to quantify the impact of the use of different parameterization schemes on regional climate model outputs, hindcast experiments have been completed applying the Regional Climate Model version 4.3 (RegCM4.3) for the Carpathian region and its surroundings at 10-km horizontal resolution with three different cumulus convection schemes. Besides, the sensitivity of outputs for subgrid-scale processes is also studied by activating the subgrid Biosphere-Atmosphere Transfer Scheme (BATS) model within other RegCM experiments. Among the analyzed factors, RegCM is most sensitive to the applied convection scheme. The impact of closure assumption related to the used convective parameterization is secondary, while the use of subgridding has less influence on the outputs. RegCM4.3 results show improved performance over our previous model simulations but still have larger amplitude for annual precipitation cycle than the measurement-based reference data. Our validation results for temperature and precipitation suggest that for the selected region, the overall best performance is achieved when using the mixed Grell-Emanuel scheme together with Fritsch and Chappell closure.

Climatological Annual Cycle of the Salinity Budgets of the Subtropical Maxima

AbstractSix subtropical salinity maxima (Smax) exist: two each in the Pacific, Atlantic, and Indian Ocean basins. The north Indian (NI) Smax lies in the Arabian Sea while the remaining five lie in the open ocean. The annual cycle of evaporation minus precipitation (E − P) flux over the Smax is asymmetric about the equator. Over the Northern Hemisphere Smax, the semiannual harmonic is dominant (peaking in local summer and winter), while over the Southern Hemisphere Smax, the annual harmonic is dominant (peaking in local winter). Regardless, the surface layer salinity for all six Smax reaches a maximum in local fall and minimum in local spring. This study uses a multidecade integration of an eddy-resolving ocean circulation model to compute salinity budgets for each of the six Smax. The NI Smax budget is dominated by eddy advection related to the evolution of the seasonal monsoon. The five open-ocean Smax budgets reveal a common annual cycle of vertical diffusive fluxes that peak in winter. These Smax have regions on their eastward and poleward edges in which the vertical salinity gradient is destabilizing. These destabilizing gradients, in conjunction with wintertime surface cooling, generate a gradually deepening wintertime mixed layer. The vertical salinity gradient sharpens at the base of the mixed layer, making the water column susceptible to salt finger convection and enhancing vertical diffusive salinity fluxes out of the Smax into the ocean interior. This process is also observed in Argo float profiles and is related to the formation regions of subtropical mode waters.

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

Impact of increased horizontal resolution in coupled and atmosphere-only models of the HadGEM1 family upon the climate patterns of South America

This study investigates the impact of increased horizontal resolution in coupled and atmosphere-only global climate models on the simulation of climate patterns in South America (SA). We analyze simulations of the HadGEM1 model family with three different horizontal resolutions in the atmosphere—N96 (~135 km at 50°N), N144 (~90 km) and N216 (~60 km)—and two different resolutions in the ocean—1° and 1/3°. In general, the coupled simulation with the highest resolution (60 km in the atmosphere and 1/3° in the ocean) has smaller systematic errors in seasonal mean precipitation, temperature and circulation over SA than the atmosphere-only model at all resolutions. The models, both coupled and atmosphere-only, properly simulate spatial patterns of the seasonal shift of the Intertropical Convergence Zone (ITCZ), the formation and positioning of the South Atlantic Convergence Zone (SACZ), and the subtropical Atlantic and Pacific highs. However, the models overestimate rainfall, especially in the ITCZ and over the western border of high-elevation areas such as southern Chile. The coupling, combined with higher resolution, result in a more realistic spatial pattern of rain, particularly over the Atlantic ITCZ and the continental branch of the SACZ. All models correctly simulate the phase and amplitude of the annual cycle of precipitation and air temperature over most of South America. The overall results show that despite some problems, increasing the resolution in the HadGEM1 model family results in a more realistic representation of climate patterns over South America and the adjacent oceans.

Spatial Variability of the Background Diurnal Cycle of Deep Convection around the GoAmazon2014/5 Field Campaign Sites

AbstractThe isolation of the Amazon rain forest makes it challenging to observe precipitation forming there, but it also creates a natural laboratory to study anthropogenic impacts on clouds and precipitation in an otherwise pristine environment. Observations were collected upwind and downwind of Manaus, Brazil, during the “Observations and Modeling of the Green Ocean Amazon 2014–2015” experiment (GoAmazon2014/5). Besides aircraft, most of the observations were point measurements made in a spatially heterogeneous environment, making it hard to distinguish anthropogenic signals from naturally occurring spatial variability. In this study, 15 years of satellite data are used to examine the spatial and temporal variability of deep convection around the GoAmazon2014/5 sites using cold cloud tops (infrared brightness temperatures colder than 240 K) as a proxy for deep convection. During the rainy season, convection associated with the inland propagation of the previous day’s sea-breeze front is in phase with the diurnal cycle of deep convection near Manaus but is out of phase a few hundred kilometers to the east and west. Convergence between the river breezes and the easterly trade winds generates afternoon convection up to 10% more frequently (on average ~4 mm day−1 more intense rainfall) at the GoAmazon2014/5 sites east of the Negro River (T0e, T0t/k, and T1) relative to the T3 site, which was located west of the river. In general, the annual and diurnal cycles of precipitation during 2014 were similar to climatological values that are based on satellite data from 2000 to 2013.

Recent and Projected Annual Cycles of Temperature and Precipitation in the Northeast United States from CMIP5

Abstract A case study is presented using the northeast United States to evaluate information contained in the monthly mean annual cycle that has yet to be exploited. This research documents the performance and projections for the northeast United States from a suite of 16 climate models in the archive of phase 5 of the Coupled Model Intercomparison Project (CMIP5) from the World Climate Research Programme (WCRP). Analysis is performed for the late twentieth-century monthly mean annual cycle and changes in the late twenty-first century. A weak seasonality in temperature and a strong seasonality in precipitation changes are found. The seasonality of changes is distinct from the mean annual cycles, such that temperature increases are largest in midwinter (December–February) and late summer [July–September (JAS)]. Precipitation increases peak in late winter–early spring (February–April), associated with increased moisture convergence and a more active storm track, and exhibit greatest model disagreement in late summer (JAS) when the models suggest weak divergence and a westward extension of the Atlantic subtropical anticyclone. The late summer–early fall maximum in temperature and late winter–early spring maximum in precipitation changes have not been seen previously in annual or seasonal mean analyses. Yet there is model agreement in these results, indicating that there is important information in the annual cycle for understanding the changes in the physical climate system and for evaluating impacts and adaptation strategies. It is argued that improved understanding of seasonal transitions has potential to increase confidence in projections, and to provide additional information of use to the impacts and decision-maker communities.

Simulation of temperature and precipitation climatology for the CORDEX-MENA/Arab domain using RegCM4

The performance of a regional climate model RegCM4.3.4 (RegCM4) in simulating the climate characteristics of the Middle East and North Africa (MENA) region has been evaluated. The simulations carried out in this study contribute to the joint effort by the international regional downscaling community called Coordinated Regional climate Downscaling Experiment (CORDEX). The model has been forced with the boundary conditions obtained from the global reanalysis dataset ERA-Interim for the period 1979–2010. An east–west cold bias is found in the northern part of the MENA domain in RegCM4 that is absent in the ERA-Interim driving forcings, whereas a large warm bias is found over the southern Arabian Peninsula (Yemen/Oman) for both RegCM4 and ERA-Interim. The possible causes leading to the warm bias over Yemen/Oman in the RegCM4 are discussed. The model performed well in capturing the salient features of precipitation which includes ITCZ, Mediterranean cyclones as well as precipitation minima over the deserts. Moreover, the annual cycles of precipitation and mean temperature over the prominent river basins of the region have been ably captured by the model. Temperature-precipitation relationship revealed that the ERA-Interim driving forcings stay closer to the observations; however, RegCM4 remains competent for most of the Koppen-Geiger climate classification types. Performance of the model in capturing the near surface winds and specific humidity is also presented. Based on the results of this study, it is concluded that RegCM4 is well suited to conduct long-term high-resolution climate change projection for the future period over the CORDEX-MENA/Arab domain.

Regional climate change projections of streamflow characteristics in the Northeast and Midwest U.S.

Abstract Study region Northeast and Midwest, United States. Study focus Assessing the climate change impacts on the basin scale is important for water and natural resource managers. Here, the presence of monotonic trends and changes in climate-driven simulated 3-day peak flows, 7-day low flows, and mean base flows are evaluated in the Northeast and Midwest U.S. during the 20th and the 21st centuries using climate projections from sixteen climate models. Proven statistical methods are used to spatially and temporally disaggregate precipitation and temperature fields to a finer resolution before being used as drivers for a hydrological model. New hydrological insights for the region Changes in the annual cycle of precipitation are likely to occur during the 21st century as winter precipitation increases and warmer temperatures reduce snow coverage across the entire domain especially in the northern basins. Maximum precipitation intensities are projected to become more intense across the region by mid-century especially along the coast. Positive trends in 3-day peak flows are also projected in the region as a result of the more intense precipitation, whereas the magnitude of 7-day low flows and mean base flows are projected to decrease. The length of the low flows season will likely extend by mid-century despite the increased precipitation as the atmospheric demand increases.

Projeções de mudanças na precipitação e temperatura no nordeste brasileiro utilizando a técnica de downscaling dinâmico

RESUMO Este trabalho apresenta análises de projeções de mudanças nos campos de precipitação e temperatura em simulações de downscaling dinâmico no contexto do projeto CORDEX. O domínio da simulação corresponde às Américas Tropicais, mas a região de estudo se restringe a duas sub-regiões do Nordeste Brasileiro: Norte (NNEB) e Sul (SNEB). O modelo regional utilizado nas simulações foi o RAMS6.0, forçado por dados do modelo global HadGEM2-ES. Foram analisados os períodos presente e três "fatias de tempo" futuras sob o cenário climático RCP8.5. Para a precipitação e temperatura no clima presente, a simulação foi comparada com os dados do CRU com finalidade de avaliar o desempenho e os erros de viés dos modelos. O RAMS6.0 mostra-se superior ao HadGEM2-ES em aspectos como, a representação da fase do ciclo anual de precipitação e temperatura, redução do viés seco na estação seca sobre o NNEB e distribuição espacial de ambas as variáveis, especialmente temperatura. Entretanto, o RAMS6.0 também exacerba alguns erros do modelo global, como o viés úmido na estação chuvosa. No clima futuro, foram analisadas as mudanças nos valores climatológicos e nos campos anuais das duas variáveis. Alguns padrões projetados pelos dois modelos incluem redução da precipitação no inverno austral e aumento da temperatura no decorrer do século.

Identification of drought phases in a 110-year record from Western Mediterranean basin: Trends, anomalies and periodicity analysis for Iberian Peninsula

The Iberian Peninsula (IP), located in a transition area between temperate and subtropical latitudes, has marked temporal and spatial variability of precipitation between its various climatic zones. Therefore, the peninsula is particularly sensitive to climate change owing to frequent periods of precipitation deficit together with societal dependence on water. In this study, we address meteorological droughts of the peninsula between 1901 and 2010, using the Global Precipitation Climatology Center database. First, we carried out a statistical classification of the peninsula according to annual precipitation cycle. The spatiotemporal variability of droughts was evaluated using the Standardized Precipitation Index (SPI) by determining the evolution of areas affected by severe and extreme drought. Subsequently, we calculated the overall trend of precipitation and anomalies to investigate whether an observed drought increase is attributable to a decrease of precipitation or an increase of precipitation extremes. Finally, we examined periodicities of precipitation anomalies via wavelet analysis, relating these to large-scale modes such as the North Atlantic Oscillation (NAO). The results show an increase in the area affected by severe and extreme drought, particularly on Atlantic-facing slopes. The mainland areas have longer and more intense periods of drought, with an average SPI of −0.52 and 4-month duration. Over the 110years analyzed, we observed weak trends of annual precipitation in the extreme northwest and southern IP. However, in the last decades of the series, long periods of strong negative anomalies are seen, interspersed with years of strong positive anomalies, suggesting an increase in precipitation pattern extremes. Finally, the relationship between the NAO index and precipitation anomalies on the Atlantic seaboard is highlighted. Thus, in both series we found a 5–6-year periodicity in their first years, with a diminishing cycle period reaching a periodicity of 2–3years in the final years. This confirms the existence of regular temporal cycles in which droughts alternate with wet periods modulated by large-scale modes.

The annual cycle of snowfall at Summit, Greenland

AbstractWhile snow accumulation over central Greenland has been extensively studied, interannual variability of snowfall in the region is not well understood due to a dearth of observations. The Integrated Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS) project at Summit, Greenland, offers a unique, ground‐based opportunity to study precipitation in central Greenland where the surface mass balance is positive. Combining data from a Precipitation Occurrence Sensor System (POSS), Millimeter‐wavelength Cloud Radar (MMCR), and snow stake field, the annual cycle of precipitation at Summit is examined. Average daily snowfall is higher by a factor of 3 from June to October compared to November to May, while surface height change is only higher by 15% during the same timeframes. This reduced variability in surface height is explained by the seasonally varying nature of latent heat flux, compaction, and wind contributions. The ICECAPS remote sensors and stake field measurements do not agree as far as total annual water equivalent. This discrepancy is likely due to a low bias in the POSS and MMCR snowfall retrievals for Summit. To further examine the seasonal cycle, snowfall measurements by the POSS were linked to local meteorological parameters, including wind direction, liquid water path (LWP), 2 m temperature, and precipitable water vapor. An observed wind direction and moisture dependence are consistent with snowfall being linked to pulses of moist air that originate over nearby, ice‐free ocean, a resource that becomes more readily available in summertime as the winter sea ice retreats. LWP is shown to have little relationship to snowfall, indicating that ice‐phase precipitation processes are quite important for snowfall at Summit.

Caracterización del “veranillo” en dos cuencas de la vertiente del Pacífico de Costa Rica, América Central

<p>The Eastern Tropical Pacific region is characterized by climate features rarely observed in tropical regions, one of them is the Mid-Summer Drought (MSD), “veranillo” or “canícula” in Spanish. On the Pacific slope of Central America, the annual precipitation cycle is characterized by two rainfall maxima in June and September-October, an extended dry season from November to May, and a shorter reduced precipitation period during July–August (MSD), during July, the magnitude of the trade winds increases and this is associated also with the Caribbean Low Level Jet (CLLJ), but characterization of these features using monthly data is difficult. In this work, seven daily gauge stations records, located at two important river basins of Costa Rica, Tarcoles and Tempisque, were studied to characterize the MSD from 1937 to 2012. Among the aspects considered are the MSD Start, Timing, End, Duration, Intensity and Magnitude. The modulation and seasonal predictability of these aspects by climate variability sources as Equatorial Eastern Pacific was lately explored, showing that warmer (cooler) conditions in Niño 3.4 tend to be associated to drier (wetter) MSD events. Rev. Biol. Trop. 62 (Suppl. 4): 1-15. Epub 2014 Diciembre 01.</p><div> </div>

Entendendo o tempo e o clima na América do Sul

A América do Sul (AS) possui uma geografia diversificada, propícia ao desenvolvimento e atuação de diferentes sistemas atmosféricos que contribuem para não-homogeneidade espacial e temporal da precipitação. Diante disso, os objetivos deste estudo são: (a) discutir os conceitos básicos de tempo e clima, (b) apresentar a climatologia de precipitação no continente sul-americano e (c) descrever os sistemas atmosféricos que contribuem para os diferentes ciclos anuais de precipitação nos diversos setores da AS, com base em revisão da literatura. De modo geral, a estação chuvosa da AS é o verão e a seca, o inverno. Nessas estações do ano, diferentes sistemas atmosféricos são responsáveis pela precipitação.

Spatial distribution of precipitation annual cycles over South Africa in 10 CORDEX regional climate model present-day simulations

This study presents an evaluation of the ability of 10 regional climate models (RCMs) participating in the COordinated Regional climate Downscaling Experiment-Africa to reproduce the present-day spatial distribution of annual cycles of precipitation over the South African region and its borders. As found in previous studies, annual mean precipitation is quasi-systematically overestimated by the RCMs over a large part of southern Africa south of about 20°S and more strongly over South Africa. The spatial analysis of precipitation over the studied region shows that in most models the distribution of biases appears to be linked to orography. Wet biases are quasi-systematic in regions with higher elevation with inversely neutral to dry biases particularly in the coastal fringes. This spatial pattern of biases is particularly obvious during summer and specifically at the beginning of the rainy season (November and December) when the wet biases are found to be the strongest across all models. Applying a k-means algorithm, a classification of annual cycles is performed using observed precipitation data, and is compared with those derived from modeled data. It is found that the in-homogeneity of the spatial and temporal distribution of biases tends to impact the modeled seasonality of precipitation. Generally, the pattern of rainfall seasonality in the ensemble mean of the 10 RCMs tends to be shifted to the southwest. This spatial shift is mainly linked to a strong overestimation of convective precipitation at the beginning of the rainy season over the plateau inducing an early annual peak and to an underestimation of stratiform rainfall in winter and spring over southwestern South Africa.

CORDEX‐NA: factors inducing dry/wet years on the North American Monsoon region

ABSTRACTThe output of four regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX)‐North America (NA) region was analysed for the 1990–2008 period, with particular interest on the mechanisms associated with wet and dry years over the North American Monsoon (NAM) core region. All RCMs (RCA3.5, HadGEM3‐RA, REMO, and RegCM4) were forced by the ERA‐Interim reanalysis. Model precipitation was compared against several observational gridded data sets at different time scales. Most RCMs capture well the annual cycle of precipitation and outperform ERA‐Interim, which is drier than the observations. RCMs underestimate (overestimate) the precipitation over the coastal plains (mountains) and have some problems to reproduce the interannual variability of the monsoon. To further investigate this, two extreme summers that showed the largest consistency among observations and RCMs were chosen: one wet (1990) and one dry (2005). The impact of the passage of tropical cyclones, the size of the Western Hemisphere Warm Pool (WHWP), the Intertropical Convergence Zone (ITCZ) position, and the initial intensity of the land–sea thermal contrast (LSTC) were analysed. During the wet year, the LSTC was stronger than the 2005 dry monsoon season and there were a larger number of hurricanes near the Gulf of California, the WHWP was more extended, and the ITCZ was located in a more northerly position than in 2005. All these processes contributed to a wetter NAM season. During the dry year, the LSTC was weaker, with a later onset, probably due to a previous very wet winter. The inverse precipitation relationship between winter and summer in the monsoon region was well captured by most of the RCMs. RegCM4 showed the largest biases and HadGEM3‐RA the smallest ones.

Regional aspects of future precipitation and meteorological drought characteristics over Southern South America projected by a CMIP5 multi‐model ensemble

ABSTRACTThis article addresses the regional impacts of climate change on precipitation and meteorological drought over Southern South America (SSA) through a CMIP5 multi‐model ensemble based on 15 General Circulation Models (GCMs) forced under two different greenhouse gas concentration pathways (RCP4.5 and RCP8.5). An assessment of the biases in the representation of the precipitation annual cycle was performed over the 1979–2008 period over five regions within SSA, based on a comparison between the GCMs precipitation outputs with the Global Precipitation Climatology Centre (GPCC) dataset. The multi‐model ensemble well reproduces the shape of the annual cycle of precipitation over most of SSA, although the monthly totals were overestimated (underestimated) over the North‐West and South (North‐East and Central‐East) regions. Changes in precipitation and meteorological drought characteristics were identified by the difference for early (2011–2040) and late (2071–2100) 21st century values with respect to the 1979–2008 baseline, using the standardized precipitation index as a short‐ and long‐term drought indicator. Future climate conditions are expected to modify the regional characteristics of meteorological droughts over SSA, but the range of uncertainty in the expected changes is high. A significant increase in the number of drought events in all the regions for most of the 21st century sub‐periods is projected for the multi‐model ensemble. The mean duration of drought events will be shorter, with no significant changes in the severity of droughts and the occurrence of multi‐decadal changes in the number of critical dry months is likely, although the significance in the changes depends on the region, future time horizon and greenhouse gas concentration pathways. These results overlap with a projected increase in precipitation over most of the regions, which has a strong seasonality and, therefore, will have some implications upon the future meteorological drought developments and the agricultural and hydrological practices in SSA.