Rainfall Trend Analysis Research Articles

Analysis of rainfall and temperature trends in northeast India

AbstractThe northeast region (NER) of India covers an area of 0.26 million km2. This region is one of the highest rainfall‐receiving regions on the planet. Consequently, it has huge water and hydropower potential and analysis of rainfall and temperature trends would be of interest to water and energy planners. Trends in monthly, seasonal, and annual rainfall and temperature on the subdivision and regional scale for the NER were examined in this study. Trend analysis of rainfall data series for 1871–2008 did not show any clear trend for the region as a whole, although there are seasonal trends for some seasons and for some hydro‐meteorological subdivisions. Similar analysis for temperature data showed that all the four temperature variables (maximum, minimum, and mean temperatures and temperature range) had rising trend. Notably for the post‐monsoon season, the Sen's estimator of slope ( °C/year) was 0.019, 0.011, and 0.015 for the maximum, minimum, and mean temperature, respectively. Copyright © 2012 Royal Meteorological Society

Detecting changes in streamflow after partial woodland clearing in two large catchments in the seasonal tropics

summary We used daily rainfall and streamflow time series from two large catchments in the seasonal tropics of Queensland, Australia to investigate the hydrological impacts of woodland clearing. The Comet catchment (16,440 km 2 ) had 45% of the native woodland cleared during the mid-1960s. In the Upper Burdekin catchment (17,299 km 2 ) clearing decreased native woodland extent from 83% to 58% between 1998 and 2009. An earlier modelling study concluded that clearing in the Comet catchment increased annual streamflow by more than 40%. Here, several published inference methods to separate land use effects from climate variability were applied. Trend analysis of daily rainfall and streamflow data showed that interannual changes in mean streamflow in the Comet catchment were mostly due to changes in rainfall. In particular, a series of La Nina events after clearing led to an unusual lack of dry periods and an apparently associated temporary increase in runoff coefficient. The overriding importance of climate variability was further confirmed using a conceptual framework that was used to interpret changes in the long-term coupled water–energy budget. Even so, there was some evidence for a slight increase in streamflow for the first few years after clearing. Fitting a Budyko-type model for two climatically similar pre- and postclearing periods (1920–1953 and 1979–2007) did not suggest a considerable change in the catchment water balance after clearing. Analysis of daily streamflow metrics did reveal some changes however, with enhanced peak flows and reduced low flows. In the Upper Burdekin catchment, trend analysis revealed a change in baseflow dynamics after clearing, while event storm flow for large rainfall events increased. In summary, woodland clearing in northern Queensland appears to have had a smaller impact on mean and interannual streamflow than might be expected from studies at sites and in small experimental catchments, but changes in daily streamflow patterns do suggest a modest change in catchment dynamics.

Extreme Climatic Variability in North-western Nigeria: An Analysis of Rainfall Trends and Patterns

Some aspects of the climate of north-western Nigeria were examined in this study, focusing more on rainfall, its inter- and intra-annual variability and patterns of distribution. Adopting the statistical distributions commonly used to describe climate states such as the mean, the standard deviation and the coefficient of variability, the climate of north-western Nigeria was analyzed for possible shifts in mean conditions and patterns. The study found that climatic conditions in north-western Nigeria have altered substantially as four drought episodes took place within the last three decades of the 20 th Century and, the 1984 drought-year rainfall was 58.8 percent lower than the long-term mean rainfall. The study further showed that the 1968 to 2008 mean rainfall shifted downwards by 8.8 percent from the long-term mean, although it cannot be said if the shift is permanent or temporary since recent rainfall trends tend to suggest a recovery. Possible options for stabilizing the regional climate are suggested.

Trend and spectral analysis of rainfall over India during 1901–2000

[1] The spectral analysis of gridded rainfall data obtained from 1384 rain gauge stations by India Meteorological Department demonstrates not much change in low-frequency components of decadal spectra of all India and its four subregions, namely, southwest, southeast, central, and northwest, during the last 10 decades. However, the dominant as well as the significant cycles lying between the periods 10–20 days, 20–30 days, 30–40 days, and 40–50 days are highly variable on an interdecadal basis. On close inspection, it can be inferred that the 40–50 day oscillations that corresponds to Madden-Julian Oscillations is mainly associated with the southern Indian region, namely southwest and southeast, and the 30–40 day oscillation of southeast region is gradually increasing on a decadal scale during the last 4 decades. The physical context of interdecadal variability of rainfall in India can be linked with the warm phase of Atlantic multidecadal oscillations and the cold phase of interdecadal Pacific oscillations. The correlogram analysis shows the presence of 15, (17, 19), and 17 year cycles for the southwest, central, and northwest regions, respectively. No significant trend is discernable during the last 10 decades, when the linear least squares fitting method and Mann-Kendall statistic to identify the trend and the normalized test statistic and statistical probability to quantify the significance of the trend are applied, on the annual rainfall data for all India and its subregions.

Trend analysis of rainfall in Bharathapuzha River basin, Kerala, India

AbstractKnowing the variations in the general rainfall pattern of a river basin is vital to understanding the hydrological cycle and water budget of the basin. The present study examined the general rainfall pattern in Bharathapuzha River basin of Malabar coast of Kerala, using monthly rainfall data for 34 years collected from 28 rain gauge stations. We used Mann‐Kendal's rank correlation statistics and wavelet analysis to examine the trend of rainfall. The annual rainfall, southwest monsoon, and pre‐monsoon rainfall of the basin shows a significant decrement towards the later years of the study. We assume that the global climate and the local environmental changes are the chief factors for the variation. Copyright © 2010 Royal Meteorological Society

Analysis of trends in the Sahelian ‘rain-use efficiency’ using GIMMS NDVI, RFE and GPCP rainfall data

Rain-use efficiency (RUE; the ratio of vegetation productivity to annual precipitation) has been suggested as a measure for assessing land degradation in arid/semi-arid areas. In the absence of anthropogenic influence, RUE has been reported to be constant over time, and any observed change may therefore be attributed to non-rainfall impacts. This study presents an analysis of the decadal time-scale changes in the relationship between a proxy for vegetation productivity (ΣNDVI) and annual rainfall in the Sahel-Sudanian zone of Africa. The aim is to test the quality of data input and the usefulness of both the RUE approach and an alternative method for separating the effects on vegetation productivity of rainfall change and human impact. The analyses are based on earth observation of both rainfall (GPCP (Global Precipitation Climatology Project), 1982–2007 and RFE (Rainfall Estimate) (1996–2007)) and ΣNDVI (AVHRR GIMMS NDVI dataset, 1982–2007). It is shown that the increase in ΣNDVI has been substantial in the Sahel-Sudanian zone over the 1982–2007 period, whereas for the period 1996–2007 the pattern of ΣNDVI trends is more complex. Also, trend analysis of annual rainfall from GPCP data (2.5° resolution) and RFE data (0.1° resolution) suggests that rainfall has increased over both periods. Further it is shown that RUE values are highly correlated to rainfall, undermining the use of earth observation (EO)-based RUE (using ΣNDVI) as a means of separating rainfall impacts from other factors. An alternative method identify temporal trends in residuals of ΣNDVI, after regressing it against annual rainfall, is tested, yet is shown to be useful only where a high correlation between ΣNDVI and annual rainfall exists. For the areas in the Sahel-Sudanian zone for which this condition is fulfilled, trend analyses suggest very limited anthropogenic land degradation in the Sahel-Sudanian zone.

Analysis of long-term rainfall trends in India

The study of precipitation trends is critically important for a country like India whose food security and economy are dependent on the timely availability of water. In this work, monthly, seasonal and annual trends of rainfall have been studied using monthly data series of 135 years (1871–2005) for 30 sub-divisions (sub-regions) in India. Half of the sub-divisions showed an increasing trend in annual rainfall, but for only three (Haryana, Punjab and Coastal Karnataka), this trend was statistically significant. Similarly, only one sub-division (Chattisgarh) indicated a significant decreasing trend out of the 15 sub-divisions showing decreasing trend in annual rainfall. In India, the monsoon months of June to September account for more than 80% of the annual rainfall. During June and July, the number of sub-divisions showing increasing rainfall is almost equal to those showing decreasing rainfall. In August, the number of sub-divisions showing an increasing trend exceeds those showing a decreasing trend, whereas in September, the situation is the opposite. The majority of sub-divisions showed very little change in rainfall in non-monsoon months. The five main regions of India showed no significant trend in annual, seasonal and monthly rainfall in most of the months. For the whole of India, no significant trend was detected for annual, seasonal, or monthly rainfall. Annual and monsoon rainfall decreased, while pre-monsoon, post-monsoon and winter rainfall increased at the national scale. Rainfall in June, July and September decreased, whereas in August it increased, at the national scale. Citation Kumar, V., Jain, S. K. & Singh, Y. (2010) Analysis of long-term rainfall trends in India. Hydrol. Sci. J. 55(4), 484–496.

Rainfall and temperature trend analysis in the red and lateritic zone of West Bengal

Due to inherent problems of water holding capacity of soil in the red and lateritic zone, the trend of climate change was assessed. Twenty rain gauge stations covering three districts (namely Bankura, Birbhum and Purulia) in the zone were considered to study the rainfall pattern. An increasing trend of yearly rainfall and shifting pattern of rainfall were observed in the said zone as a whole. The rainfall during May decreased in most of the selected stations, where as in October the rainfall amount increased in 75 % cases and in November it increased in 95 % cases. Analysis of maximum temperature data shows that average monthly temperature of summer months (April – May) of 1990-2000 decreased marginally compared to that of 1970-80 .The minimum temperature of the zone, as a whole shows an increasing trend.

Trend analysis of Indian summer monsoon rainfall at different spatial scales

AbstractThe results obtained from a conventional trend analysis of the Indian summer monsoon rainfall over a larger region are contradicted when analysis is performed at a finer resolution because of spatial variability and heterogeneity in the rainfall pattern. The present study analyzes the trend of summer monsoon rainfall all over India at a finer spatial resolution (1° latitude × 1° longitude) to identify the places that have a significant trend in terms of both rainfall amount and occurrence. The results obtained from this study are compared with those of a recent study by Goswami et al. (2006), where trend analysis is performed over a larger region [Central India (CI); 10° latitude × 12° longitude; assumed to be homogeneous in that study]. The increasing trend of occurrence of heavy rainfall and decreasing trend of occurrence of moderate rainfall, as concluded from that study, are contradicted by the present results for some places in CI. The present analysis shows spatially varying mixed responses of global warming toward rainfall occurrence and amounts all over India. The perception of increase in daily rainfall amount and occurrence due to climate change is found to be not correct for some of the regions in India. The possible reason may be the spatial variability of local changes such as rapid urbanization, industrialization and deforestation. Copyright © 2009 Royal Meteorological Society

An analysis of late twentieth century trends in Australian rainfall

AbstractTrends in Australian precipitation from 1970 to 2006 are examined using a daily rainfall dataset. Results suggest a linkage between changes in the monsoon trough and rainfall trends over northwestern Australia. The late twentieth century drought observed along the Queensland coast is a response to changes in the atmospheric circulation that generates anomalous subsidence at high and middle levels of the atmosphere, thus inhibiting convection over the region. In addition, an anomalous anticyclonic circulation at low levels over Queensland tends to weaken the easterlies in the tropical western Pacific, thus diminishing the transport of moist air onto the coast. Trends in the frequency and magnitude of different rainfall events are also examined. This reveals that changes in total rainfall are dominated by trends in very heavy rainfall events across Australia. For example, some parts of western Australia reveal an increase in heavy rainfall events that are not accompanied by a rise in modest rainfall events, resulting in changes in the shape of the distribution towards a more skewed precipitation distribution. On the other hand, the frequency of extreme rainfall events along the Queensland coast has declined during summer and autumn consistently with the total rainfall decrease, indicating changes in the position of the precipitation distribution rather than its shape. Copyright © 2008 Royal Meteorological Society

Spatial and temporal characteristics of evaporation trends over India during 1971-2000

Evaporation and rainfall data for the period 1971-2000 for 58 well distributed stations over India were selected for this study. Trends of these two parameters for the country as a whole and for individual stations for annual (January – December), winter (December, January and February), summer (March – May), monsoon (June – September) and post-monsoon (October, November) period were analysed and tested for significance at 95% level of confidence. The analysis shows that for the country as a whole, the evaporation has significantly decreased in all seasons while there is no significant trend in rainfall. Out of 58 stations, numbers of stations having significant decrease in evaporation are 45 (annual), 30 (winter), 42 (summer) and 35 (monsoon and post monsoon seasons). Decadal analysis of trends shows that the variability of evaporation towards the decreasing trend is steadily maintained throughout the period but more in the decade 1991-2000. Spatial analysis of the seasonal trends of evaporation indicates the decreasing trends over all parts of India except northeast where it is increasing. Regions of significant decrease in evaporation viz., North, Southwest and Southeast and increase in evaporation viz., Northeast emerge from the spatial analysis of trends over the country. Spatial analysis of seasonal rainfall trends indicates the increasing trends in southern parts and decreasing trends in central and northeastern parts of the country. Evaporation trends of nearly 50% stations (mostly in southern parts of India) show complimentary relation with rainfall of the same period. Rest of the long term trends in evaporation may be due to the variation in other parameters like wind speed, cloud cover, sunshine duration etc. which needs further examination.

Trend analysis of rainfall in the headstreams of the Zambezi River Basin in Zambia

Changes in catchment response as a result of climate change and/or variability continue to be of concern to hydrologists and water managers and thus identification and study of changes in rainfall as a major input into the hydrologic system remains pivotal in water resources management and planning for reliable input into modelling catchment response systems. An attempt has been made in this study to analyse long-term rainfall data obtained from five rain gauges (Kabompo, Kasempa, Mwinilunga, Mongu and Kaoma) located in the headstream regions of the Zambezi river basin in Zambia and to determine if these time series belonged to similar regime, have had any significant trends and if there was any homogeneity in trends among stations. To detect change in regime, the data were separately subjected to intervention analysis (using Cumulative Summation or CUSUM technique) and step change analysis (using rank-sum test) and subsequently the trend in each of the time series were determined using Mann–Kendall-statistic. The analyses undertaken to identify possibility of any intervention due to either natural and/or man-made causes, through the CUSUM technique, did not show signs of any major interventions except for Mongu station, where a change in regime was observed around 1980. This was even confirmed through step change analysis using the rank-sum test. Though the five stations showed marginal downward trends, these were not significant. Even, the test of homogeneity in trends observed at different stations showed homogeneity between them. Based on these findings, it was concluded that the rainfall data in the entire sub-basin belonged to a similar climate regime and the rainfall data for the entire period could be used for developing rainfall-response relationship except for Mongu, where the time series from 1981 onwards appear to have been subjected human/instrumental errors and needs to be investigated and updated.

Trend analysis of winter rainfall over southern Québec and new Brunswick (Canada)

Winter rainfall is a non‐negligible issue for urban drainage in Canada as it can generate significant flooding, especially when it occurs at the same time as high air temperature and in the presence of an appreciable snow cover. According to climate change scenarios, it is expected that the occurrence of these events will increase in a future climate. The purpose of this paper is to perform a trend analysis on six indices related to winter rainfall (January–February) at 60 weather stations located in southern Québec and New Brunswick (Canada) in order to detect possible trends in the frequency or intensity of winter rainfall events during the twentieth century. Datasets were provided by Environment Canada and come from the Canadian Daily Rehabilitated Precipitation Database. The bootstrap‐based Mann‐Kendall test is used to detect possible non‐stationarities in the dataset, while Sen's slope estimator is used to quantify the magnitude of the slope. Results show that 19 stations out of 60 present a significant trend (18 of them being positive) at a 5% level for winter (January–February) total rainfall. In most cases where a trend was detected for winter rainfall there was also an increase in the number of days with rainfall (42% of the stations). These results suggest that globally, for the region under study, rainfall during January and February was more likely to occur, often resulting in a significant increase in the total rainfall during these months. Increasing trends in maximum daily rainfall during January and February were also observed for 9 stations (15% of the stations). The spatial distribution of stations where significant trends were detected is consistent with the hypothesis that trends in winter rainfall are more likely to be observed for stations located in the southern part of the region under study.

TRENDS IN RAINFALL TOTAL AND VARIABILITY (1970–2000) ALONG THE KWAZULU-NATAL DRAKENSBERG FOOTHILLS

ABSTRACT South Africa's most valuable source of water is the eastern escarpment region of the KwaZulu-Natal Drakensberg and Lesotho highlands. These upper catchments supply much of KwaZulu-Natal, feed the Vaal River in the interior through two inter-basin transfer schemes and are important conservation areas. Analysis of rainfall and rainfall variability trends can thus contribute to a better understanding and management of the area and yet no recent studies have investigated these aspects. This study assesses the 1970–2000 rainfall period using 13 stations to the east of the escarpment in KwaZulu-Natal and presents a spatial perspective on annual rainfall totals and intra- and inter-annual variability. Altitude and distance from the escarpment eastward are found to influence total annual rainfall with an increase of 41.5 mm per 100m in altitude between approximately 1100m and 2100m a.s.l., and a corresponding decrease of 54 mm for every 10 km eastward from the escarpment. Neither inter- nor intra-annual rainfall variability is influenced directly by altitude or the relation to the escarpment. Latitudinal position is found to have no significant affect on station totals but variability increases from south to north in the Drakensberg, possibly related to the greater seasonal contribution by frontal rains in the south, or more variable annual storm activity in the north.

An analysis of long-term rainfall variability, trends and groundwater availability in the Mulunguzi river catchment area, Zomba mountain, Southern Malawi

Annual rainfall series and annual base flow series (1954–1998) derived from the annual river flow series for the Mulunguzi river in Malawi were analysed using the non-parametric Mann–Whitney Pettit and Mann–Whitney–Wilcoxon statistics to detect any trends and variability patterns. A general decline in rainfall, with alternating wet and drier years was detected since 1954. The variation pattern mainly followed the El Nino and Southern Oscillation and the La Nina episodes. Two rainfall change points were detected at 1965 and 1979 after which the rainfall declined. The rainfall trend and variation pattern was evident in the base flow series, indicating a strong correlation between the rainfall and base flow series. This strong correlation means that the Zomba mountain aquifer, the source of the Mulunguzi river mainly depends on rainfall for recharge. Hence all water resources development and planning activities in the catchment area should take into consideration the effects of climate variability on water yield.

Statistical analysis of rainfall distribution and trend of rainfall anomalies districtwise during monsoon period over West Bengal

The statistical analysis of rainfall distributions in different districts of West Bengal during monsoon period for 68 years (1931-98) have been studied in this paper. The statistical parameters such as moments, coefficient of skewness and kurtosis have been computed to understand the nature of such rainfall distribution in each district. The rainfall anomalies during monsoon period (June–September) have also been studied for each district of two meteorological Sub-divisions, Sub-Himalayan West Bengal (SHWB) and Gangetic West Bengal (GWB) by fitting regression lines through ‘Least Square Method’ and results for rainfall trends for each district of West Bengal have been discussed in this paper.

Monitoring rainfall trends to predict adverse impacts—a case study from Sri Lanka (1964–1993)

This paper describes an analysis of long-term rainfall trends in central mountainous region of Sri Lanka. A 30-year 60 rain gauge data set is analyzed to identify the trends in annual and seasonal rainfall. Inter-annual as well as intra-annual rainfall trends are investigated to understand the adverse impacts on water resources, floods and land degradation. It is found that there is a decrease in the annual rainfall in the region, while different seasons show mixed results. The March–April 1st inter-monsoon period shows the highest decrease in rainfall where almost all the rain gauges have recorded decreasing rainfall. In addition to the decreasing rainfall trend, the numbers of rainy days have reduced giving rise to an increasing rain intensity trend. In order to understand better the changes to rain intensity-frequency relation, a universal multifractal analysis was carried out where multifractal models calibrated to first and last decades of the rain series are used to estimate the intensity–frequency relations in the rainfall series. The results show that there is a decrease of inter-monsoon rainfall, while the intensities and return period of extreme events appear to become shorter. These changes could be associated with regional climate changes, and are consistent with projections related to Asia Brown Cloud phenomena.

Analysis of rainfall trends and dry periods on a pluviometric gradient representative of Mediterranean climate in the Duero Basin, Spain

The present work studies the trends in rainfall and the behaviour of dry spells along a pluviometric gradient representative of the conditions of the Mediterranean region. The region is characterized by a marked water deficit in the summer, a pronounced irregularity in its rainfall regime, and a noteworthy frequency of dry spells or periods without appreciable rainfall. The results obtained confirm the general previsions of the IPCC, with a predominance of dry years over wet ones and a negative rainfall trend in the central sector. An increase in intra-annual variability in rainfall, and a very pronounced occurrence of dry periods independent of the total annual rainfall, are also seen. These circumstances will potentially increase the vulnerability of several Mediterranean ecosystems located along the gradient that are currently subject to considerable pressure from human activities; this will increase the environmental problems of these zones (agro-forestry–grazing productivity, soil degradation, recharge of aquifers, forest fires, runoff models, biological diversity and composition, etc.).

Spatial analysis of rainfall trends in the region of Valencia (east Spain)

This paper examines the spatial and temporal rainfall characteristics of the region of Valencia, Western Mediterranean Basin (east Spain), during the World Meteorological Organization (WMO) normal period 1961‐1990. The study used a dense and homogeneous daily precipitation database comprising 97 rain-gauge stations. Total and monthly rainfall concentrations have been studied in the context of their mean values, interannual variability and spatial diversification. Trends have been analysed using both parametric and non-parametric tests. In order to establish the spatial distribution of rainfall patterns and to detect homogeneous areas with similar rainfall evolution, %

1946-1988年の夏季アジアモンスーンの長期変動

An observational study has been made of the long-term variability of Asian summer monsoon rainfall for the period 1946-1988 and its relationship to global sea-surface temperatures (SSTs) and geopotential height fields. The trend analysis of June-September rainfall for the recent four decades shows a distinct long-term trend in rainfall over several Asian regions; increasing trends in southwest India, and decreasing trends in northwest and central India, on the south side of the Himalayas, and in the western Indochina peninsula facing the Bay of Bengal. A rotated empirical orthogonal function (R-EOF) analysis was applied to global SSTs for the above 43-year period (Shinoda and Kawamura, 1994). The second R-EOF (R-EOF2) mode exhibits the warming trend of the Indian Ocean. The correlation analysis between the time coefficients of the R-EOF2 mode and monsoon rainfall shows that the trend components which are observed in both the R-EOF2 mode and rainfall for the above areas are responsible for the high correlation between them. The R-EOF2 mode is highly correlated not only with monsoon rainfall, but also with tropical 850 hPa geopotential heights. This correlation pattern exhibits an east-west contrast having positive correlations over Africa and the western Pacific Ocean and negative correlations over the northern Indian Ocean. The above positive and negative correlations coincide with the increasing and decreasing trends in 850 hPa heights. Over the Indian subcontinent, areas having negative and positive trends of 850 hPa heights coincide with those having increasing and decreasing trends in regional rainfall, respectively. On a monthly basis, for June and August, the Indian subcontinent is extensively covered with areas having increasing trends in rainfall and decreasing trends in 850 hPa heights, whereas the areas are limited to southwest India during July and September.