Rainfall deficit and excess within Oltenia region, Romania (1961-2020)

The aim of this study was to evaluate the influence of atmospheric precipitation on the yield of spring malting barley. The plant height and heading of the studied forms were observed as additional indicators of their reaction to variable water conditions. The plant material for this study consisted of spring barley breeding lines in generations F6-F7 evaluated at 7 locations in 1996-2001. The highest yield was observed with precipitation within the range 258-321 or 356-382 mm per growing season in years with colder or warm weather, respectively. These results were obtained using abundant plant material highly differentiated genetically, so it may be inferred that the above values are the rainfall levels optimal for spring barley cultivation under Polish climatic conditions. The experimental locations could be divided into four classes according to observations on mean yields and on total rainfall before heading and between heading and full maturity. the optimal class included locations where the highest yield was observed; in the second there was a high precipitation level but a lower yield was obtained; in the third class there was a shortage of rainfall before heading, and in the fourth class there was a shortage of rainfall between heading and maturity. The observation of yields lower than those obtained in optimal locations led to the assumption that stress factors at these locations did not allow the yield potential of the studied genotypes to be fully expressed. The studied genotypes showed good adaptation to the variable conditions of the Polish climate, which is characterized by periods with a shortage or excess of rainfall.

Simulation of ambient parameters using Grell convective scheme to study rainfall heterogeneity over western India

Monthly rainfall over Kerala state showed an increasing tendency during October and November with a decrease in December. Such trend was more evident since 1961 onwards. Overall, over Kerala State, there was an increase of 96.7 mm in northeast monsoon rainfall over a period of time, indicating an increase of 20.1 per cent against the normal rainfall of 481.5 mm and significant at 5 per cent level. Rainfall during December was highly variable and undependable, which is of great concern in plantation crop production of the State of Kerala. As a whole, 34.0 per cent (46 years out of 135) of the years recorded either excess or deficit rainfall. The monthly rainfall range as well as its variability was less during excess rainfall years when compared to that of deficit rainfall years. The study also revealed that El Nino/La Nina events had weak teleconnection with excess/deficit northeast monsoon rainfall over Kerala.

ABSTRACTRainfall over Myanmar has large inter‐annual variability causing droughts and floods in many years. In this study, rainfall variability (in monthly scale) over Myanmar during summer monsoon has been examined using observed data. It is found that monthly rainfall in June, July and August months do not have any relation among each other, indicating that monthly rainfall received in Myanmar in these 3 months vary due to different mechanisms. In order to develop an effective drought monitoring and prediction system for the country, such mechanisms of rainfall variability have to be studied. Using composite wind analysis for excess and deficit rainfall years, it is found that deficiency of rainfall occurs when south‐westerly winds at 850 hPa are weaker over the region in June. During excess rainfall years, south‐westerly wind anomalies seen in June turn to stronger and milder westerly winds in July and August, respectively. However, a cyclonic anomaly is seen over North Bay of Bengal adjoining western coast of Myanmar in all the 3 months. It is found that the Myanmar rainfall is correlated positively with the sea surface temperature over central Pacific Ocean. An empirical orthogonal function (EOF) analysis of monthly and seasonal mean rainfall over the region has been carried out. The leading mode (EOF‐1) shows coherent spatial patterns between the Indian monsoon rainfall over east and central parts of the India and rainfall over the western Pacific. The second leading mode of seasonal rainfall shows a trend in rainfall during the study period.

In this paper, a diagnostic study is carried out with global analysis data sets to determine how the large scale atmospheric circulation affecting the anomalous drought of the Indian summer monsoon 2002. The daily analysis obtained from National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) for the month of July is used to investigate the mean circulation characteristics and the large scale energetics over the Indian monsoon domain. Examination of rainfall revealed that the summer monsoon (JJAS) rainfall of 2002 over India is 22% below normal in which the large deficit of 56% below normal rainfall in July. The recent past drought during summer season of 2004 and 2009 are 12 and 23%, respectively, below normal rainfall. The large deficit of rainfall in 2009 is from the June month with 48% below normal rainfall, where as 2004 drought contributed from July (19%) and August (24%). Another significant facet of the rainfall in July 2002 is lowest ever recorded in the past 138 years (1871–2008). The circulation features illustrated weak low level westerly wind at 850 hPa (Somali Jet) in July during large deficit rainfall years of 1987 and 2002 with a reduction of about 30% when compared with the excess and normal rainfall years of 1988 and 2003. Also, tropical easterly jet at 150 hPa reduced by 15% during the deficit rainfall year of 2002 against the excess rainfall year of 1988. Both the jet streams are responsible for low level convergence and upper level divergence leading to build up moisture and convective activity to sustain the strength of the monsoon circulation. These changes are well reflected in reduction of tropospheric moisture profile considerably. It is found that the maximum number of west pacific cyclonic system during July 2002 is also influenced for large deficit rainfall over India. The dynamic, thermodynamic and energetic clearly show the monsoon break type situation over India in the month of July 2002 resulting less convective activity and the reduction of moisture. The large diabatic heating, flux convergence of heat and moisture over south east equatorial Indian Ocean are also responsible for drought situation in July 2002 over the Indian region.

When rain matters! Investments and value relevance

Spatial and time behaviours of rainfall shortage and excess are analysed for Catalonia (NE Spain) using a database obtained from 99 rain gauges with monthly totals collected from 1961 to 1990. The distribution of monthly amounts for each rain gauge is modelled by means of the gamma or Poisson‐gamma distributions. Then, using an equiprobable transformation, monthly amounts described with these distributions are substituted by values given by the Standardized Precipitation Index (SPI), which follows a standardized normal distribution and provides a unique pluviometric scale. After that, principal component analysis (PCA) is applied to the set of monthly SPIs. A double regionalization of the 99 rain gauges, distinguishing between episodes of rainfall shortage and excess, is achieved by taking into account the rotated factor loadings (RFL) correlating rain gauges and principal components (PC). A time classification of rainfall shortage and excess episodes is also established, considering in this case the factor scores (FS) obtained after a PCA of variables based on monthly SPIs. The spatial regionalization achieved becomes a rough picture of the different topographic domains (Pyrenees, Pre‐Pyrenees, Central Basin, Littoral and Pre‐Littoral chains and Mediterranean coast), the climatic diversity of Catalonia being enhanced by these results. The time clustering suggests a quite complex behaviour of the rainfall shortage and excess episodes. Moreover, the spatial distribution of these time clusters is very disperse, in such a way that monthly shortage and excess sometimes affect the whole of Catalonia and sometimes just a small area. Besides results obtained from PCA and clustering algorithms, it is worth noticing that the severity of the episodes increases remarkably only for rainfall shortage. In addition, an analysis of the number of rain gauges affected by monthly shortage and excess shows an interesting fact: whereas the number of rain gauges associated with a shortage has an increasing tendency, a significant decreasing tendency for excess is detected in the period 1961–1990. Copyright © 2001 Royal Meteorological Society

The present study has examined the combined effect of MJO, ENSO and IOD on the intraseasonal and interannual variability of northeast monsoon rainfall over south peninsular India. The study has revealed that the intraseasonal variation of daily rainfall over south peninsular India during NEM season is associated with various phases of eastward propagating MJO life cycle. Positive rainfall anomaly over south peninsular India and surrounding Indian Ocean (IO) is observed during the strong MJO phases 2, 3 and 4; and negative rainfall anomaly during the strong MJO phases 5,6,7,8 and 1. Above normal (below normal) convection over south peninsular India and suppressed convection over east Indian and West Pacific Ocean, high pressure (low pressure) anomaly over West Pacific Ocean, Positive (negative) SST anomalies over equatorial East and Central Pacific Ocean and easterly wind anomaly (westerly anomaly) over equatorial Indian Ocean are the observed features during the first three MJO (5, 6, 7) phases and all these features are observed in the excess (drought) NEMR composite. This suggests that a similar mode of physical mechanism is responsible for the intraseasonal and interannual variability of northeast monsoon rainfall. The number of days during the first three phases (last four phases) of MJO, where the enhanced convection and positive rainfall anomaly is over Indian Ocean (East Indian ocean and West Pacific Ocean), is more (less) during El Nino and IOD years and less during La Nina and NIOD years and vice versa. The observed excess (deficit) rainfall anomaly over west IO and south peninsular India and deficit (excess) rainfall anomaly over east IO including Bay of Bengal and West Pacific Ocean suggest that the more (less) number of first three phases during El Nino and IOD (La Nina and Negative IOD) is due to the interaction between eastward moving MJO and strong easterlies over equatorial IO present during El Nino and IOD years. This interaction would inhibit the development of long duration MJO and would result in short duration high frequency MJO type which confined over Indian Ocean and south peninsular India and hence make all the El Nino and IOD years to be excess rainfall years for NEM season.

Rainfall and temperature are the most important environmental factors influencing crop growth, development, and yield. The northwestern (NW) part of India is one of the main regions of food grain production of the country. It comprises of six meteorological subdivisions (Haryana, Punjab, West Rajasthan, East Rajasthan, Gujarat and Saurashtra, Kutch and Diu). In this study, attempts were made to study variability and trends in rainfall and temperature during 30-year climate normal periods (CN) and 10-year decadal excess or deficit rainfall frequency during the historical period from 1871 to 2016. The Mann-Kendall and Spearman’s rank correlation (Spearman’s rho) tests were used to determine significance of trends. Least square linear fitting method was adopted to find out the slopes of the trend lines. The long-term mean annual rainfall over North West India is 587.7 mm (standard deviation of 153.0 mm and coefficient of variation 26.0). There was increasing trend in minimum and maximum temperatures during post monsoon season in entire study period and current climate normal period (1991–2016) due to which the sowing of rabi season crops may be delayed and there may be germination problem too. There was a non-significant decreasing trend in rainfall during monsoon season and an increasing trend in rainfall during post monsoon over North West India during entire study period. During current CN5 (1991–2016), all the subdivision (except the Saurashtra region) showed a decreasing trend in rainfall during monsoon season which is a matter of concern for kharif crops and those rabi crops which are grown as rainfed on conserved soil moisture. The decadal annual and seasonal frequencies of excess and deficit years results revealed that the annual total deficit rainfall years (24) exceeded total excess rainfall years (22) in North West India during the entire study period. While during the current decadal period (2011 to 2016), single year was the excess year and 2 years were deficit rainfall years in all subdivisions (except East Rajasthan) on annual basis.

Is the Indian monsoon rainfall linked to the Southern Ocean sea ice conditions?

The present study aims to provide information regarding the temporal distribution of important physical-chemical parameters that affect water chemistry. Graphical representation is recorded for important physiochemical variables to understand groundwater quality and ecological status of the groundwater systems over a period of time in Dindigul district, Tamil Nadu. The Dindigul District monthly rainfall data were collected from the Public Works Department (PWD), Surface and Groundwater Division, Govt. of Tamil Nadu. After 1995, that there was a gradual increase in the rainfall pattern and the excess rainfall was recorded as 1018.59 mm, 1052.82 mm, 1073.73mm during the years 1996, 2008, 2010 respectively. The lowest rainfall of 588.51mm was recorded in 2012. Apart from excess rainfall years, all the other cases recorded the minimum rainfall and showed the decreasing trend from1995 to 2012. After 1990s, release of untreated waste water from Tannery industry in to the water ways and lands - contaminated the groundwater. The change in the rainfall pattern and quantity played important role in the salinity of the groundwater. After 1995s, the NO3value of 16.8mg L-1 was recorded during 2010. Accordingly, it had the highest excess rainfall of 1073.73 mm, during 2010. Deficit rainfall in 2000 ranges from 337.67mm, the NO3 value of 68.8 mg L-1 was recorded. The chemical characteristics of ground water are determined by the level of contribution from the geological sources and infiltration water from the surface sources. Monitoring of pollution patterns and its trends with respect to urbanization is an important task for achieving sustainable management of groundwater.

Importance of integration of subseasonal predictions to improve climate services in Sri Lanka case study: Southwest monsoon 2019

ABSTRACTThis study has investigated the influence of the decadal component of the Pacific Decadal Oscillation (PDO) on the Indian monsoon in observations and coupled climate model. A major part of the conventionally defined PDO is shown to be dominated by interannual variability. By extracting the pure decadal part of the North Pacific variability, this study has shown that the Indian monsoon rainfall exhibits different relations with the conventionally defined PDO and the pure decadal component of the PDO. This result may have implications for decadal prediction of the monsoon. The analysis suggests that the warm (cold) phase of pure decadal variability of PDO is associated with deficit (excess) rainfall over the west central part of India. In contrast, the conventional warm (cold) PDO index is associated with deficit (excess) rainfall over most of India. The warm phase of the pure decadal PDO opposes the moisture flow beyond 20°N over the Indian monsoon region via the meridional winds extending from the North Pacific and leads to reduced rainfall over west central India. The Community Climate System Model version 4 of the National Center for Atmospheric Research shows reasonable simulation of the decadal PDO mode in both the North Pacific sea surface temperature and the Indian monsoon rainfall and the relation between them. Further, the observed and simulated PDO–monsoon relation is substantiated through a regionally de‐coupled experiment. The coupled model experiment also provides supporting evidence for the mechanism involving the intermediary role played by the tropical Pacific Ocean in the PDO–monsoon relation.

<p>Hydrology plays a pivotal role in the geomorphology and carbon balance of tropical peatlands. The alteration of the hydrological processes due to climate and/or land cover change might result in significant impacts to this ecosystem. Therefore, improved understanding of tropical peatland hydrology is critical in order to evaluate their fate under current and future climate and ultimately to develop sustainable peatland management practices. However, due to its complexity related to various flow interactions and anthropogenic interferences, comprehensive hydrological studies based on measured field data on tropical peatlands are still limited. Alternatively, hydrological models have been used to simulate the major components of the hydrological processes and to answer “what-if” questions.</p><p>In this context, a fully distributed and physically-based MIKE SHE model was used to simulate the water balance within Padang Island in the eastern coast of Sumatra, Indonesia. The island is characterized as a mosaic landscape of natural forest, forest plantation and smallholder agriculture. Comprehensive data set from field measurements including high resolution digital terrain model derived from airborne LiDAR were used for the model development. The model was calibrated and validated against observed groundwater level and stream flow data distributed across the island. The simulation was performed using current climate data that cover a distinct dry and wet year. The subsidence impacts were investigated by simulating the future projection up to 50 years. Further, additional scenario was developed to represent the pre-existing condition without agriculture and forestry practices to evaluate the land cover change impacts.</p><p>The results show that the water balance is predominantly controlled by climatic variables. The evapotranspiration accounts for the main water loss representing 50 – 80 % of the total annual rainfall. The amount of evapotranspiration remains relatively constant in the temporal basis irrespective to the rainfall, which means that the magnitude and direction of the remaining hydrological flow paths are driven by the balance between rainfall and evapotranspiration. In the dry period with a rainfall deficit, the water storage is depleted in order to meet the evapotranspiration demand. In the wet period, the excess rainfall is transformed into overland flow, base flow and positive storage change which contributes to increased inundation frequency.</p><p>The future projection indicates that there is a shift in the hydrological flow path, as the overland flow increases and the groundwater flow decreases due to the changing topography from peat subsidence. However, the hydrological flow path of the natural forest in the central part of the island remains relatively intact. The agriculture and forestry practice doesn’t significantly alter the hydrological flow path compared to the pre-existing condition. In addition, the boundary impact to the natural forest is not apparent under the wet period, while it gets more prominent in the dry period (~300 meter under current condition).</p><p>Our results, which are among the first comprehensive hydrological studies for the tropical peatlands, should help to improve the understanding of landscape scale hydrological processes in tropical peatland, which is relevant for scientists and policymakers to develop science-based peatland management practices.</p>

The study was based on data collected from nine stations of the Institute of Meteoro­logy and Water Management in central-eastern Poland (1971-2005) concerning monthly precipitation total and mean monthly air temperature during the vegetation period of early potatoes (April-July). Optimal precipitation for early potato was calculated according to the Klatt indexes for medium cohesive and light soils in the successive months of the vegetation period. Rainfall deficit and excess rainfall were determined based on differences between monthly precipitation totals recorded in the years of the study and values considered to be optimal. It was found that the frequency of rainfall deficit during vegetation of early potato in each analysed location both for medium cohesive soil and for light soil exceeded the frequency of its excess. The greatest mean monthly rainfall deficit from the multiannual period in the vegetation season of early potato in all the analysed locations and for both soil types was recorded in June, while excess rainfall was observed in July. Lower values of standard deviation for rainfall deficit were calculated in the case of light soil than medium cohesive soil, while an opposite dependence was recorded for excess rainfall. The risk for early potato plantations on light soil was connected with frequent extreme deficits. They were observed most often in the south-eastern part of the study area, while they were rarest in the belt from Pułtusk towards Szepietowo. Values of the slope of the trend lines were low for all the weather stations and most of them were statistically non-significant. However, all values concerning rainfall deficit were negative, which indicates its slight increase from year to year. A significant trend for changes in rainfall deficit was observed only in Włodawa and Siedlce, while for excess rainfall it was found in Szepietowo and Białowieża.