scholarly journals An assessment of the skill of downscaled GCM outputs in simulating historical patterns of rainfall variability in South Africa

2013 ◽  
Vol 45 (1) ◽  
pp. 134-147 ◽  
Author(s):  
D. A. Hughes ◽  
S. Mantel ◽  
T. Mohobane
Keyword(s):  
South Africa ◽  
Water Resources ◽  
General Circulation ◽  
Hydrological Model ◽  
Rainfall Variability ◽  
General Circulation Models ◽  
Local Scale ◽  
Coastal Areas ◽  
General Applicability ◽  
Modelling Studies

Uncertainties associated with General Circulation Models (GCMs) and the downscaling methods used for regional or local scale hydrological modelling can result in substantial differences in estimates of future water resources availability. This paper assesses the skill of nine statistically downscaled GCMs in reproducing historical climate for 15 catchments in five regions of South Africa. The identification of skilled GCMs may reduce the uncertainty in future predictions and the focus is on rainfall skill as the GCMs show very similar patterns of change in temperature. The skill tests were designed to assess whether the GCMs are able to realistically reproduce precipitation distribution statistics and patterns of seasonality, persistence and extremes. Some models are consistently less skilful for the regions assessed, while some are generally more skilful with some regionally specific exceptions. There are differences in the GCMs skill across the different regions and in the skill ranking between coastal areas and inland regions. However, only a limited reduction in uncertainty is achieved when using only the downscaled GCM outputs identified as being skilled in a hydrological model for one of the regions. Further modelling studies are required to determine the general applicability of this observation.

scholarly journals The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

2015 ◽  
Vol 15 (14) ◽  
pp. 7797-7818 ◽  
Author(s):  
N. P. Hindley ◽  
C. J. Wright ◽  
N. D. Smith ◽  
N. J. Mitchell
Keyword(s):  
Southern Ocean ◽  
Gravity Wave ◽  
General Circulation ◽  
Hot Spot ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Wave Drag ◽  
Southern Andes ◽  
Analysis Technique ◽  
Modelling Studies

Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

scholarly journals An Investigation into the Future Changes in Onset and Cessation of Rain and Their Variability over the Aswa Catchment, Uganda

Climate ◽  
2020 ◽  
Vol 8 (6) ◽  
pp. 67
Author(s):  
Michael Iwadra ◽  
P. T. Odirile ◽  
B. P. Parida ◽  
D. B. Moalafhi
Keyword(s):  
General Circulation ◽  
Rainfall Variability ◽  
Standardized Precipitation Index ◽  
Tropical Rainfall Measuring Mission ◽  
Kendall Test ◽  
Close Correlation ◽  
General Circulation Models ◽  
Extreme Precipitation Events ◽  
Future Global Warming ◽  
The Future

Future global warming may result in extreme precipitation events leading to crop, environment and infrastructure damage. Rainfall is a major input for the livelihood of peasant farmers in the Aswa catchment where the future rainfall variability, onset and cessation are also likely to be affected. The Aswa catchment has limited rainfall data; therefore, use of secondary datasets from Tropical Rainfall Measuring Mission (TRMM) is considered in this study, based on the close correlation of the recorded and TRMM rainfall. The latter was used to calibrate the statistical downscaling model for downscaling of two general circulation models to simulate future changes in rainfall. These data were analyzed for trends, wet and dry conditions/variability; onset and cessations of rain using the Mann–Kendall test, Standardized Precipitation Index (SPI) and the cumulative percentage mean rainfall method, respectively. Results show future rainfall is likely to increase, accompanied by increasing variability reaching as high as 118.5%. The frequency of SPI values above 2 (extreme wetness) is to increase above current level during mid and end of the century. The highest rainfall variability is expected especially during the onset and cessation months, which are generally expected to come earlier and later, by up to four and five weeks, respectively. The reliability worsens from the midterm (2036–2065) to long term (2066–2099). These likely changes in rainfall quantities, variability, onset and cessation months are some of the key rainfall dynamics that have implications for future arable agriculture, environment and water resource availability and planning over the Aswa catchment, as is increasingly the case elsewhere.

scholarly journals Uncertainty Analysis of Monthly Precipitation in GCMs Using Multiple Bias Correction Methods under Different RCPs

2020 ◽  
Vol 12 (18) ◽  
pp. 7508 ◽  
Author(s):  
Young Hoon Song ◽  
Eun-Sung Chung ◽  
Mohammed Sanusi Shiru
Keyword(s):  
South Korea ◽  
Bias Correction ◽  
General Circulation ◽  
General Circulation Models ◽  
Coastal Areas ◽  
Historical Period ◽  
Monthly Precipitation ◽  
Opposite Pattern ◽  
Statistical Measures ◽  
Selection Of

This study quantified the uncertainties in historical and future average monthly precipitation based on different bias correction methods, General Circulation Models (GCMs), Representative Concentration Pathways (RCPs), projection periods, and locations within the study area (i.e., the coastal and inland areas of South Korea). The GCMs were downscaled using deep learning, random forest, and nine quantile mapping bias correction methods for 22 gauge stations in South Korea. Data from the Korean Meteorology Administration (1970–2005) were used as the reference data in this study. Two statistical measures, the standard deviation and interquartile range, were used to quantify the uncertainties. The probability distribution density was used to assess the similarity/variation in rainfall distributions. For the historical period, the uncertainty in the selection of bias correction methods was greater than that in the selection of GCMs, whereas the opposite pattern was observed for the projection period. The projection period had the lowest level of uncertainty in the selection of RCP scenarios, and for the future, the uncertainly related to the time period was slightly lower than that for the other sources but was much greater than that for the RCP selection. In addition, it was clear that the level of uncertainty of inland areas is much lower than that of coastal areas. The uncertainty in the selection of the GCMs was slightly greater than that in the selection of the bias correction method. Therefore, the uncertainty in the selection of coastal areas was intermediate between the selection of bias correction methods and GCMs. This paper contributes to an improved understanding of the uncertainties in climate change projections arising from various sources.

scholarly journals How well do general circulation models represent low-frequency rainfall variability?

2014 ◽  
Vol 50 (3) ◽  
pp. 2108-2123 ◽  
Author(s):  
Eytan Rocheta ◽  
Michael Sugiyanto ◽  
Fiona Johnson ◽  
Jason Evans ◽  
Ashish Sharma
Keyword(s):  
General Circulation ◽  
Rainfall Variability ◽  
Low Frequency ◽  
General Circulation Models

scholarly journals The Interannual Variability of the Onset of the Maize Growing Season over South Africa and Zimbabwe

2005 ◽  
Vol 18 (16) ◽  
pp. 3356-3372 ◽  
Author(s):  
M. A. Tadross ◽  
B. C. Hewitson ◽  
M. T. Usman
Keyword(s):  
South Africa ◽  
Early Onset ◽  
General Circulation ◽  
Decadal Variability ◽  
Late Onset ◽  
Growing Season ◽  
General Circulation Models ◽  
Self Organizing Map ◽  
Asymmetric Component ◽  
Synoptic Conditions

Abstract Subsistence farmers within southern Africa have identified the onset of the maize growing season as an important seasonal characteristic, advance knowledge of which would aid preparations for the planting of rain-fed maize. Onset over South Africa and Zimbabwe is calculated using rainfall data from the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the Computing Center for Water Research (CCWR). The two datasets present similar estimates of the mean, standard deviation, and trend of onset for the common period (1979–97) over South Africa. During this period, onset has been tending to occur later in the season, in particular over the coastal regions and the Limpopo valley. However, the CCWR data (1950–97) indicate that this is part of long-term (decadal) variability. Characteristic rainfall patterns associated with late and early onset are estimated using a self-organizing map (SOM). Late onset is associated with heavier rainfall over the subcontinent. When onset is early over Zimbabwe, there is an increased frequency of more intense rainfall over northeast Madagascar during the preceding August. Accompanying these intense events is an increased frequency of positive 500-hPa geopotential height anomalies to the southeast of the continent. Similar positive height anomalies are also frequently present during early onset. The study indicates that onset variability is partly forced by synoptic conditions, and the successful use of general circulation models to estimate onset will depend on their simulation of the zonally asymmetric component of the westerly circulation.

scholarly journals Assessing the Spatial Pattern of Irrigation Demand under Climate Change in Arid Area

2020 ◽  
Vol 9 (9) ◽  
pp. 506
Author(s):  
Liping Wang ◽  
Shufang Wang ◽  
Liudong Zhang ◽  
Mohamed Khaled Salahou ◽  
Xiyun Jiao ◽  
...  
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Spatial Pattern ◽  
General Circulation ◽  
General Circulation Models ◽  
Northwest China ◽  
Arid Areas ◽  
Irrigation Demand ◽  
Balance System ◽  
Rcp 8.5

Studying the pattern of agricultural water demand under climate change has great significance for the regional water resources management, especially in arid areas. In this study, the future pattern of the irrigation demand in Hotan Oasis in Xinjiang Uygur Autonomous Region in Northwest China, including Hotan City, Hotan County, Moyu County and Luopu County, was assessed based on the general circulation models (GCMs) and the Surface Energy Balance System model (SEBS). Six different scenarios were used based on the GCMs of BCC_CSM1.1, HadGEM2-ES and MIROC-ESM-CHEM under the Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. The results showed that the method integrating the GCMs and SEBS to predict the spatial pattern was useful. The irrigation demand of Hotan Oasis will increase in 2021–2040. The annual irrigation demand of Hotan City is higher, with 923.2 and 936.2 mm/a in 2021–2030 and 2031–2040, respectively. The other three regions (Hotan County, Moyu County and Luopu County) are lower in the six scenarios. The annual irrigation demand showed a spatial pattern of high in the middle, low in the northwest and southeast under the six scenarios in 2021–2040. The study can provide useful suggestions on the water resources allocation in different regions to protect water resources security in arid areas.

scholarly journals The Importance of High-Frequency Sea Surface Temperature Variability to the Intraseasonal Oscillation of Indian Monsoon Rainfall

2008 ◽  
Vol 21 (23) ◽  
pp. 6119-6140 ◽  
Author(s):  
Nicholas P. Klingaman ◽  
Peter M. Inness ◽  
Hilary Weller ◽  
Julia M. Slingo
Keyword(s):  
High Frequency ◽  
General Circulation ◽  
Climate Models ◽  
Indian Monsoon ◽  
Rainfall Variability ◽  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Propagation Speed ◽  
General Circulation Models ◽  
Atmospheric Model

Abstract While the Indian monsoon exhibits substantial variability on interannual time scales, its intraseasonal variability (ISV) is of greater magnitude and hence of critical importance for monsoon predictability. This ISV comprises a 30–50-day northward-propagating oscillation (NPISO) between active and break events of enhanced and reduced rainfall, respectively, over the subcontinent. Recent studies have implied that coupled general circulation models (CGCMs) were better able to simulate the NPISO than their atmosphere-only counterparts (AGCMs). These studies have forced their AGCMs with SSTs from coupled integrations or observations from satellite-based infrared sounders, both of which underestimate the ISV of tropical SSTs. The authors have forced the 1.25° × 0.83° Hadley Centre Atmospheric Model (HadAM3) with a daily, high-resolution, observed SST analysis from the United Kingdom National Center for Ocean Forecasting that contains greater ISV in the Indian Ocean than past products. One ensemble of simulations was forced by daily SSTs, a second with monthly means, and a third with 5-day means. The ensemble with daily SSTs displayed significantly greater variability in 30–50-day rainfall across the monsoon domain than the ensemble with monthly mean SSTs, variability similar to satellite-derived precipitation analyses. Individual ensemble members with daily SSTs contained intraseasonal events with a strength, a propagation speed, and an organization that closely matched observed events. When ensemble members with monthly mean SSTs displayed power in intraseasonal rainfall, the events were weak and disorganized, and they propagated too quickly. The ensemble with 5-day means had less intraseasonal rainfall variability than the ensemble with daily SSTs but still produced coherent NPISO-like events, indicating that SST variability at frequencies higher than 5 days contributes to but is not critical for simulations of the NPISO. It is concluded that high-frequency SST anomalies not only increased variance in intraseasonal rainfall but helped to organize and maintain coherent NPISO-like convective events. Further, the results indicate that an AGCM can respond to realistic and frequent SST forcing to generate an NPISO that closely resembles observations. These results have important implications for simulating the NPISO in AGCMs and coupled climate models, as well as for predicting tropical ISV in short- and medium-range weather forecasts.

scholarly journals Potential Climate Change Impacts on Water Resources in Egypt

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1715
Author(s):  
Soha M. Mostafa ◽  
Osama Wahed ◽  
Walaa Y. El-Nashar ◽  
Samia M. El-Marsafawy ◽  
Martina Zeleňáková ◽  
...  
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Irrigation Water ◽  
General Circulation ◽  
General Circulation Models ◽  
Future Climate ◽  
Future Climate Change ◽  
Impact Of Climate Change ◽  
Water Demands ◽  
The Impact

This paper presents a comprehensive study to assess the impact of climate change on Egypt’s water resources, focusing on irrigation water for agricultural crops, considering that the agriculture sector is the largest consumer of water in Egypt. The study aims to estimate future climate conditions using general circulation models (GCMs), to assess the impact of climate change and temperature increase on water demands for irrigation using the CROPWAT 8 model, and to determine the suitable irrigation type to adapt with future climate change. A case study was selected in the Middle part of Egypt. The study area includes Giza, Bani-Sweif, Al-Fayoum, and Minya governorates. The irrigation water requirements for major crops under current weather conditions and future climatic changes were estimated. Under the conditions of the four selected models CCSM-30, GFDLCM20, GFDLCM21, and GISS-EH, as well as the chosen scenario of A1BAIM, climate model (MAGICC/ScenGen) was applied in 2050 and 2100 to estimate the potential rise in the annual mean temperature in Middle Egypt. The results of the MAGICC/SceGen model indicated that the potential rise in temperature in the study area will be 2.12 °C in 2050, and 3.96 °C in 2100. The percentage of increase in irrigation water demands for winter crops under study ranged from 6.1 to 7.3% in 2050, and from 11.7 to 13.2% in 2100. At the same time, the increase in irrigation water demands for summer crops ranged from 4.9 to 5.8% in 2050, and from 9.3 to 10.9% in 2100. For Nili crops, the increase ranged from 5.0 to 5.1% in 2050, and from 9.6 to 9.9% in 2100. The increase in water demands due to climate change will affect the water security in Egypt, as the available water resources are limited, and population growth is another challenge which requires a proper management of water resources.

scholarly journals The ability of a GCM-forced hydrological model to reproduce global discharge variability

2010 ◽  
Vol 7 (1) ◽  
pp. 687-724 ◽  
Author(s):  
F. C. Sperna Weiland ◽  
L. P. H. van Beek ◽  
J. C. J. Kwadijk ◽  
M. F. P. Bierkens
Keyword(s):  
General Circulation ◽  
Hydrological Model ◽  
General Circulation Models ◽  
The Arctic ◽  
Climate Data ◽  
Mean Values ◽  
Ensemble Mean ◽  
Runoff Variability ◽  
Abstract Data ◽  
Impacts Of Climate Change

Abstract. Data from General Circulation Models (GCMs) are often used in studies investigating hydrological impacts of climate change. However GCM data are known to have large biases, especially for precipitation. In this study the usefulness of GCM data for hydrological studies was tested by applying bias-corrected daily climate data of the 20CM3 control experiment from an ensemble of twelve GCMs as input to the global hydrological model PCR-GLOBWB. Results are compared with discharges calculated from a model run based on a reference meteorological dataset constructed from the CRU TS2.1 data and ERA-40 reanalysis time-series. Bias-correction was limited to monthly mean values as our focus was on the reproduction of runoff variability. The bias-corrected GCM based runs resemble the reference run reasonably well, especially for rivers with strong seasonal patterns. However, GCM derived discharge quantities are overall too low. Furthermore, from the arctic regimes it can be seen that a few deviating GCMs can bias the ensemble mean. Moreover, the GCMs do not well represent intra- and inter-year variability as exemplified by a limited persistence. This makes them less suitable for the projection of future runoff extremes.

scholarly journals Flood forecasting in Blue Nile basin using a process-based hydrological model

2014 ◽  
Vol 3 (1) ◽  
pp. 10-21
Author(s):  
Osama R Abdel-Aziz
Keyword(s):  
General Circulation ◽  
Hydrological Model ◽  
Human Life ◽  
General Circulation Models ◽  
Future Climate Change ◽  
Hydrological Process ◽  
Nile Basin ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Basin Scale

Predictions of variations in global and regional hydrological cycles and their response to changes in climate and the environment are key problems for future human life. Therefore, basin-scale hydrological forecasts, along with predictions regarding future climate change, are needed in areas with high flood potential. This study forecasts hydrological process scenarios in Blue Nile basin using a distributed hydrological model (DHM) and predicted scenarios of precipitation from two general circulation models, CCSM3 model and Miroc3.2-hires. Firstly, river discharge was simulated by the DHM using the observed rainfall from 1976 to 1979 and then, simulating future precipitations from 2011 to 2040, discharge scenarios were predicted. DOI: http://dx.doi.org/10.3126/ije.v3i1.9938 International Journal of Environment Vol.3(1) 2014: 10-21

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