scholarly journals Twentieth-Century Climate Change over Africa: Seasonal Hydroclimate Trends and Sahara Desert Expansion

2018 ◽  
Vol 31 (9) ◽  
pp. 3349-3370 ◽  
Author(s):  
Natalie Thomas ◽  
Sumant Nigam
Keyword(s):  
Twentieth Century ◽  
Source Region ◽  
Surface Air Temperature ◽  
Rain Gauge ◽  
Mitigation Strategies ◽  
Annual Rainfall ◽  
Sahara Desert ◽  
Seasonal Temperature ◽  
African Continent ◽  
Climate Simulations

Twentieth-century trends in seasonal temperature and precipitation over the African continent are analyzed from observational datasets and historical climate simulations. Given the agricultural economy of the continent, a seasonal perspective is adopted as it is more pertinent than an annual-average one, which can mask offsetting but agriculturally sensitive seasonal hydroclimate variations. Examination of linear trends in seasonal surface air temperature (SAT) shows that heat stress has increased in several regions, including Sudan and northern Africa where the largest SAT trends occur in the warm season. Broadly speaking, the northern continent has warmed more than the southern one in all seasons. Precipitation trends are varied but notable declining trends are found in the countries along the Gulf of Guinea, especially in the source region of the Niger River in West Africa, and in the Congo River basin. Rainfall over the African Great Lakes—one of the largest freshwater repositories—has, however, increased. It is shown that the Sahara Desert has expanded significantly over the twentieth century, by 11%–18% depending on the season, and by 10% when defined using annual rainfall. The expansion rate is sensitively dependent on the analysis period in view of the multidecadal periods of desert expansion (including from the drying of the Sahel in the 1950s–80s) and contraction in the 1902–2013 record, and the stability of the rain gauge network. The desert expanded southward in summer, reflecting retreat of the northern edge of the Sahel rainfall belt, and to the north in winter, indicating potential impact of the widening of the tropics. Specific mechanisms for the expansion are investigated. Finally, this observational analysis is used to evaluate the state-of-the-art climate simulations from a comparison of the twentieth-century hydroclimate trends. The evaluation shows that modeling regional hydroclimate change over the African continent remains challenging, warranting caution in the development of adaptation and mitigation strategies.

scholarly journals Striking Seasonality in the Secular Warming of the Northern Continents: Structure and Mechanisms

2017 ◽  
Vol 30 (16) ◽  
pp. 6521-6541 ◽  
Author(s):  
Sumant Nigam ◽  
Natalie P. Thomas ◽  
Alfredo Ruiz-Barradas ◽  
Scott J. Weaver
Keyword(s):  
Twentieth Century ◽  
Land Surface ◽  
Climate Models ◽  
Linear Trend ◽  
Surface Air Temperature ◽  
Cost Effective ◽  
Secular Change ◽  
Radiative Energy ◽  
Intergovernmental Panel ◽  
Climate Simulations

The linear trend in twentieth-century surface air temperature (SAT)—a key secular warming signal—exhibits striking seasonal variations over Northern Hemisphere continents; SAT trends are pronounced in winter and spring but notably weaker in summer and fall. The SAT trends in historical twentieth-century climate simulations informing the Intergovernmental Panel for Climate Change’s Fifth Assessment show varied (and often unrealistic) strength and structure, and markedly weaker seasonal variation. The large intra-ensemble spread of winter SAT trends in some historical simulations was surprising, especially in the context of century-long linear trends, with implications for the detection of the secular warming signal. The striking seasonality of observed secular warming over northern continents warrants an explanation and the representation of related processes in climate models. Here, the seasonality of SAT trends over North America is shown to result from land surface–hydroclimate interactions and, to an extent, also from the secular change in low-level atmospheric circulation and related thermal advection. It is argued that the winter dormancy and summer vigor of the hydrologic cycle over middle- to high-latitude continents permit different responses to the additional incident radiative energy from increasing greenhouse gas concentrations. The seasonal cycle of climate, despite its monotony, provides an expanded phase space for the exposition of the dynamical and thermodynamical processes generating secular warming, and an exceptional cost-effective opportunity for benchmarking climate projection models.

scholarly journals Performance of TRMM TMPA 3B42 V7 in Replicating Daily Rainfall and Regional Rainfall Regimes in the Amazon Basin (1998–2013)

2018 ◽  
Vol 10 (12) ◽  
pp. 1879 ◽  
Author(s):  
Véronique Michot ◽  
Daniel Vila ◽  
Damien Arvor ◽  
Thomas Corpetti ◽  
Josyane Ronchail ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Daily Rainfall ◽  
Rain Gauge ◽  
Rainfall Data ◽  
Annual Rainfall ◽  
Spatial Coverage ◽  
Rainfall Regimes ◽  
Trmm 3B42 ◽  
Good Agreement

Knowledge and studies on precipitation in the Amazon Basin (AB) are determinant for environmental aspects such as hydrology, ecology, as well as for social aspects like agriculture, food security, or health issues. Availability of rainfall data at high spatio-temporal resolution is thus crucial for these purposes. Remote sensing techniques provide extensive spatial coverage compared to ground-based rainfall data but it is imperative to assess the quality of the estimates. Previous studies underline at regional scale in the AB, and for some years, the efficiency of the Tropical Rainfall Measurement Mission (TRMM) 3B42 Version 7 (V7) (hereafter 3B42) daily product data, to provide a good view of the rainfall time variability which is important to understand the impacts of El Nino Southern Oscilation. Then our study aims to enhance the knowledge about the quality of this product on the entire AB and provide a useful understanding about his capacity to reproduce the annual rainfall regimes. For that purpose we compared 3B42 against 205 quality-controlled rain gauge measurements for the period from March 1998 to July 2013, with the aim to know whether 3B42 is reliable for climate studies. Analysis of quantitative (Bias, Relative RMSE) and categorical statistics (POD, FAR) for the whole period show a more accurate spatial distribution of mean daily rainfall estimations in the lowlands than in the Andean regions. In the latter, the location of a rain gauge and its exposure seem to be more relevant to explain mismatches with 3B42 rather than its elevation. In general, a good agreement is observed between rain gauge derived regimes and those from 3B42; however, performance is better in the rainy period. Finally, an original way to validate the estimations is by taking into account the interannual variability of rainfall regimes (i.e., the presence of sub-regimes): four sub-regimes in the northeast AB defined from rain gauges and 3B42 were found to be in good agreement. Furthermore, this work examined whether TRMM 3B42 V7 rainfall estimates for all the grid points in the AB, outgoing longwave radiation (OLR) and water vapor flux patterns are consistent in the northeast of AB.

scholarly journals Observations and  Modelling of Precipitation  in the Southern Alps of  New Zealand

2021 ◽  
Author(s):  
◽  
Stephen John Stuart
Keyword(s):  
New Zealand ◽  
Climate Model ◽  
Regional Climate ◽  
Rain Gauge ◽  
Southern Alps ◽  
Annual Rainfall ◽  
Mean Annual Precipitation ◽  
Mountain Range ◽  
Mountainous Regions ◽  
Orographic Rainfall

<p>Precipitation in the central Southern Alps affects glaciation, river flows and key economic activities, yet there is still uncertainty about its spatial distribution and primary influences. Long-term and future patterns of New Zealand precipitation can be estimated by the HadRM3P regional climate model (RCM) - developed by the United Kingdom Met Office - but orographic rainfall in the steep and rugged topography of the Southern Alps is difficult to simulate accurately at the 30-km resolution of the RCM. To quantify empirical relationships, observations of surface rainfall were gathered from rain gauges covering a broad region of the South Island. In four transects of the Hokitika, Franz Josef and Haast regions, the mean annual precipitation maxima of objectively interpolated profiles are consistently located 7-11 km southeast of the New Zealand Alpine Fault. The magnitude and shape of the rainfall profile across the Southern Alps are strongly influenced by the 850-hPa wind direction to the north of the mountain range, as determined by comparing rain-gauge observations to wind vectors from NCEP/NCAR Reanalysis 1. The observed profile of orographically enhanced rainfall was incorporated into a trivariate spline in order to interpolate precipitation simulated by the RCM. This downscaling method significantly improved the RCM's estimates of mean annual rainfall at stations in the Southern Alps region from 1971 to 2000, and RCM projections of future rainfall in mountainous regions may be similarly refined via this technique. The improved understanding of the observed rainfall distribution in the Southern Alps, as gained from this analysis, has a range of other hydrological applications and is already being used in 'downstream' modelling of glaciers.</p>

Extreme Rainfall Events in the Macro-Metropolis of São Paulo: trends and connection with climate oscillations

2021 ◽  
Author(s):  
Carolyne B. Machado ◽  
Thamiris L. O. B. Campos ◽  
Sameh A. Abou Rafee ◽  
Jorge A. Martins ◽  
Alice M. Grimm ◽  
...  
Keyword(s):  
Urban Areas ◽  
Extreme Rainfall ◽  
Kendall Test ◽  
Rain Gauge ◽  
Sao Paulo ◽  
Annual Rainfall ◽  
São Paulo ◽  
Wet Season ◽  
Extreme Rainfall Events ◽  
Climatic Indices

AbstractIn the present work, the trend of extreme rainfall indices in the Macro-Metropolis of São Paulo (MMSP) was analyzed and correlated with largescale climatic oscillations. A cluster analysis divided a set of rain gauge stations into three homogeneous regions within MMSP, according to the annual cycle of rainfall. The entire MMSP presented an increase in the total annual rainfall, from 1940 to 2016, of 3 mm per year on average, according to Mann-Kendall test. However, there is evidence that the more urbanized areas have a greater increase in the frequency and magnitude of extreme events, while coastal and mountainous areas, and regions outside large urban areas, have increasing rainfall in a better-distributed way throughout the year. The evolution of extreme rainfall (95th percentile) is significantly correlated with climatic indices. In the center-north part of the MMSP, the combination of Pacific Decadal Oscillation (PDO) and Antarctic Oscillation (AAO) explains 45% of the P95th increase during the wet season. In turn, in southern MMSP, the Temperature of South Atlantic (TSA), the AAO, the El Niño South Oscillation (ENSO) and the Multidecadal Oscillation of the North Atlantic (AMO) better explain the increase in extreme rainfall (R2 = 0.47). However, the same is not observed during the dry season, in which the P95th variation was only negatively correlated with the AMO, undergoing a decrease from the ‘70s until the beginning of this century. The occurrence of rainy anomalous months proved to be more frequent and associated with climatic indices than dry months.

Long-term predictability of winter teleconnection indices and their relationship to seasonal temperature extremes in Europe

2021 ◽  
Author(s):  
Nina Schuhen ◽  
Nathalie Schaller ◽  
Hannah C. Bloomfield ◽  
David J. Brayshaw ◽  
Jana Sillmann ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Surface Temperature ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Decadal Variability ◽  
Environmental Research ◽  
Seasonal Temperature ◽  
East Atlantic ◽  
Teleconnection Patterns

&lt;p&gt;European winter weather is dominated by several low-frequency teleconnection patterns, the main ones being the North Atlantic Oscillation (NAO), East Atlantic, East Atlantic/Western Russia and Scandinavian patterns. Through predicting these patterns, skillful forecasts of weather parameters like surface temperature can be generated, which in turn are used in a variety of applications (e.g., predictions of energy demand). A previous study (Weisheimer et.al., 2017) found that the NAO was subject to decadal variability during the twentieth century, affecting its long-term predictability. During recent decades, predictions for the NAO index have shown considerable skill, but this is likely to change during future periods of reduced predictability.&lt;/p&gt;&lt;p&gt;We analyze the century-long ERA-20C reanalysis and ASF-20C seasonal hindcast datasets to find if the other main teleconnection patterns also experience fluctuations in predictability, with potential implications for future skill and development of seasonal forecasting models. By linking the teleconnections to extreme cold and heat wave indices (Russo et al., 2015), we highlight the impact of these large-scale patterns on seasonal surface temperature in Europe during two periods of interest in the middle and end of the century. Our study shows that even though the predictability of the teleconnection patterns themselves fluctuates on a decadal scale, the links to winter surface temperatures are not significantly affected. However, the ability of the seasonal hindcasts to reproduce these patterns is quite limited.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Russo, S., Sillmann, J., &amp; Fischer, E. M. (2015). Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters, 10(12), 124003. doi: 10.1088/1748-9326/10/12/124003&lt;/p&gt;&lt;p&gt;Weisheimer, A., Schaller, N., O&amp;#8217;Reilly, C., MacLeod, D. A., &amp; Palmer, T. (2017). Atmospheric seasonal forecasts of the twentieth century:&amp;#160; multi-decadal variability in predictive skill of the winter North Atlantic Oscillation (NAO) and their potential value for extreme event attribution. Quarterly Journal of the Royal Meteorological Society, 143(703), 917-926. doi: 10.1002/qj.29&lt;/p&gt;

From climate change perception to bottom-up adaptation initiatives: a case study from banana producers of Upper Huallaga basin, Peru

2021 ◽  
Author(s):  
Livia Serrao ◽  
Lorenzo Giovannini ◽  
Luz Elita Balcazar Terrones ◽  
Hugo Alfredo Huamaní Yupanqui ◽  
Dino Zardi
Keyword(s):  
Climate Change ◽  
Mitigation Strategies ◽  
Annual Rainfall ◽  
Banana Plant ◽  
Adaptation Measures ◽  
Clear Trend ◽  
Bottom Up ◽  
Temperature And Precipitation ◽  
Weather Events

&lt;p&gt;Climatic characteristics and weather events have always conditioned the success of a harvest. Climate change and the associated increase in intense weather phenomena in recent years are making it clearer than ever that agriculture is among the sectors most at risk. Although problems in agriculture are found all over the world, the most vulnerable contexts are those where agriculture is low-tech and rainfed. Here, adaptation strategies are even more urgent to secure the food production. Assuming that the awareness of climate change is the basis for the adoption of adaptation and mitigation strategies, it is interesting to correlate the degree of perception of local inhabitants with their willingness to adopt bottom-up initiatives.&lt;/p&gt;&lt;p&gt;The current study focuses on banana producers&amp;#8217; perceptions of climate change in a tropical valley, and the initiatives that farmers adopt to cope with recent intense weather events. The banana plant (Musa Musacae) grows in tropical climates with annual rainfall around 2000 mm and average temperatures around 27&amp;#176;C. The species&amp;#8217; threadlike root system and the weak pseudostem make it particularly vulnerable to wind gusts, which, at speeds higher than 15 m/s, can bend and knock over entire plantations. The increased frequency of convective thunderstorms observed in connection with climate change has made downburst phenomena more frequent and caused greater crop loss.&lt;/p&gt;&lt;p&gt;The aim of the present work is to estimate the correlation between banana producers&amp;#8217; perceptions of climate change and their bottom-up initiatives for adaptation. To achieve this goal, the case study of the Upper Huallaga valley, which is located in the Peruvian Amazon region as shown in Figure 1, is analysed. The work was carried out at two levels: (i) we interviewed 73 banana producers in the valley, (ii) we estimated the alterations and trends in temperature and precipitation recorded by the only three available meteorological stations within the valley. Finally, we compared the two databases to evaluate if the perception of the population was confirmed by the data. Most of the surveyed population observed an increase in temperature, consistent with the results of the data analysis, and an increase in precipitation, which was not consistent with observations as these showed a cyclic variation without a clear trend. With regards to the adaptation measures, it was observed that, although a clear majority of the sample surveyed (around 82%) agreed with the existence of climate change, only 46% of them had taken any initiative to counteract adverse events in some way. However, it is important to note that the strategies implemented were all devised and implemented by the farmers themselves. Funding and coordinating the dissemination of these adaptation practices by the local authority through a rural development plan could certainly strengthen the population&amp;#8217;s effort.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.34e8e7df2cff59382630161/sdaolpUECMynit/12UGE&amp;app=m&amp;a=0&amp;c=59f620ca81f3a3bb7bb44139d499513c&amp;ct=x&amp;pn=gnp.elif&amp;d=1&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;Figure 1, On the left side: the Upper Huallaga basin. &lt;/em&gt;&lt;em&gt;On the right side: the study area&lt;/em&gt;&lt;/p&gt;

scholarly journals Probabilistic precipitation and temperature downscaling of the Twentieth Century Reanalysis over France

2016 ◽  
Vol 12 (3) ◽  
pp. 635-662 ◽  
Author(s):  
Laurie Caillouet ◽  
Jean-Philippe Vidal ◽  
Eric Sauquet ◽  
Benjamin Graff
Keyword(s):  
Climate Change ◽  
Twentieth Century ◽  
High Resolution ◽  
Large Scale ◽  
Local Scale ◽  
Precipitation Forecast ◽  
Seasonal Temperature ◽  
Downscaling Method ◽  
Quantitative Precipitation Forecast ◽  
Precipitation And Temperature

Abstract. This work proposes a daily high-resolution probabilistic reconstruction of precipitation and temperature fields in France over the 1871–2012 period built on the NOAA Twentieth Century global extended atmospheric reanalysis (20CR). The objective is to fill in the spatial and temporal data gaps in surface observations in order to improve our knowledge on the local-scale climate variability from the late nineteenth century onwards. The SANDHY (Stepwise ANalogue Downscaling method for HYdrology) statistical downscaling method, initially developed for quantitative precipitation forecast, is used here to bridge the scale gap between large-scale 20CR predictors and local-scale predictands from the Safran high-resolution near-surface reanalysis, available from 1958 onwards only. SANDHY provides a daily ensemble of 125 analogue dates over the 1871–2012 period for 608 climatically homogeneous zones paving France. Large precipitation biases in intermediary seasons are shown to occur in regions with high seasonal asymmetry like the Mediterranean. Moreover, winter and summer temperatures are respectively over- and under-estimated over the whole of France. Two analogue subselection methods are therefore developed with the aim of keeping the structure of the SANDHY method unchanged while reducing those seasonal biases. The calendar selection keeps the analogues closest to the target calendar day. The stepwise selection applies two new analogy steps based on similarity of the sea surface temperature (SST) and the large-scale 2 m temperature (T). Comparisons to the Safran reanalysis over 1959–2007 and to homogenized series over the whole twentieth century show that biases in the interannual cycle of precipitation and temperature are reduced with both methods. The stepwise subselection moreover leads to a large improvement of interannual correlation and reduction of errors in seasonal temperature time series. When the calendar subselection is an easily applicable method suitable in a quantitative precipitation forecast context, the stepwise subselection method allows for potential season shifts and SST trends and is therefore better suited for climate reconstructions and climate change studies. The probabilistic downscaling of 20CR over the period 1871–2012 with the SANDHY probabilistic downscaling method combined with the stepwise subselection thus constitutes a perfect framework for assessing the recent observed meteorological events but also future events projected by climate change impact studies and putting them in a historical perspective.

scholarly journals Analyses of temperature and precipitation in the Indian Jammu and Kashmir region for the 1980–2016 period: implications for remote influence and extreme events

2019 ◽  
Vol 19 (1) ◽  
pp. 15-37 ◽  
Author(s):  
Sumira Nazir Zaz ◽  
Shakil Ahmad Romshoo ◽  
Ramkumar Thokuluwa Krishnamoorthy ◽  
Yesubabu Viswanadhapalli
Keyword(s):  
Climate Change ◽  
Statistical Tests ◽  
Wrf Model ◽  
Annual Rainfall ◽  
Maximum Temperature ◽  
Seasonal Temperature ◽  
Western Himalayas ◽  
Jammu And Kashmir ◽  
Temperature And Precipitation ◽  
Average Annual Temperature

Abstract. The local weather and climate of the Himalayas are sensitive and interlinked with global-scale changes in climate, as the hydrology of this region is mainly governed by snow and glaciers. There are clear and strong indicators of climate change reported for the Himalayas, particularly the Jammu and Kashmir region situated in the western Himalayas. In this study, using observational data, detailed characteristics of long- and short-term as well as localized variations in temperature and precipitation are analyzed for these six meteorological stations, namely, Gulmarg, Pahalgam, Kokarnag, Qazigund, Kupwara and Srinagar during 1980–2016. All of these stations are located in Jammu and Kashmir, India. In addition to analysis of stations observations, we also utilized the dynamical downscaled simulations of WRF model and ERA-Interim (ERA-I) data for the study period. The annual and seasonal temperature and precipitation changes were analyzed by carrying out Mann–Kendall, linear regression, cumulative deviation and Student's t statistical tests. The results show an increase of 0.8 ∘C in average annual temperature over 37 years (from 1980 to 2016) with higher increase in maximum temperature (0.97 ∘C) compared to minimum temperature (0.76 ∘C). Analyses of annual mean temperature at all the stations reveal that the high-altitude stations of Pahalgam (1.13 ∘C) and Gulmarg (1.04 ∘C) exhibit a steep increase and statistically significant trends. The overall precipitation and temperature patterns in the valley show significant decreases and increases in the annual rainfall and temperature respectively. Seasonal analyses show significant increasing trends in the winter and spring temperatures at all stations, with prominent decreases in spring precipitation. In the present study, the observed long-term trends in temperature (∘Cyear-1) and precipitation (mm year−1) along with their respective standard errors during 1980–2016 are as follows: (i) 0.05 (0.01) and −16.7 (6.3) for Gulmarg, (ii) 0.04 (0.01) and −6.6 (2.9) for Srinagar, (iii) 0.04 (0.01) and −0.69 (4.79) for Kokarnag, (iv) 0.04 (0.01) and −0.13 (3.95) for Pahalgam, (v) 0.034 (0.01) and −5.5 (3.6) for Kupwara, and (vi) 0.01 (0.01) and −7.96 (4.5) for Qazigund. The present study also reveals that variation in temperature and precipitation during winter (December–March) has a close association with the North Atlantic Oscillation (NAO). Further, the observed temperature data (monthly averaged data for 1980–2016) at all the stations show a good correlation of 0.86 with the results of WRF and therefore the model downscaled simulations are considered a valid scientific tool for the studies of climate change in this region. Though the correlation between WRF model and observed precipitation is significantly strong, the WRF model significantly underestimates the rainfall amount, which necessitates the need for the sensitivity study of the model using the various microphysical parameterization schemes. The potential vorticities in the upper troposphere are obtained from ERA-I over the Jammu and Kashmir region and indicate that the extreme weather event of September 2014 occurred due to breaking of intense atmospheric Rossby wave activity over Kashmir. As the wave could transport a large amount of water vapor from both the Bay of Bengal and Arabian Sea and dump them over the Kashmir region through wave breaking, it probably resulted in the historical devastating flooding of the whole Kashmir valley in the first week of September 2014. This was accompanied by extreme rainfall events measuring more than 620 mm in some parts of the Pir Panjal range in the south Kashmir.

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