Trend In Annual Rainfall Research Articles

Spatial distribution and estimation of rainfall trends and erosivity in the Epit\xe1cio Pessoa reservoir catchment, Para\xedba, Brazil

The main goals of this study are to better understand the spatial and temporal variabilities in rainfall and to identify rainfall trends and erosivity for the period from 1963 to 1991 in the Epitácio Pessoa reservoir catchment, which is located in Paraíba, northeastern Brazil. This study analyzes annual rainfall trends on a regional scale by using monthly data from 13 rainfall stations. For this purpose, the nonparametric Mann–Kendall and Sen methods were used in the analysis. Descriptive statistics methods and interpolation techniques were also used for spatial–temporal analysis of the annual rainfall. A detailed statistical analysis applied to the time series of all the stations indicates that the rainfall presents substantial annual spatial–temporal variability and a negative trend (decrease) in the mean rainfall at most of the rainfall stations in the catchment during the study period. The results only showed a positive trend for the Soledade and Pocinhos stations. The distribution of positive and negative trends in the Epitácio Pessoa reservoir catchment is extremely irregular, and the changes in the study area are more significant compared to those identified in other studies.Graphic abstract

Trend Analysis of Rainfall Data in Divisional Meteorological Stations of Bangladesh

Sixty four years, 1952-2016, rainfall data (monthly rainfall and annual total rainfall) were analyzed using non-parametric methods like Mann-Kendall and Sen’s T test to detect the recent trends in rainfall pattern over seven divisions of Bangladesh. Sen’s non-parametric estimator of slope was frequently used to estimate the magnitude of trend, whose statistical significance was assessed by the Mann–Kendall test. Station basis trend analysis was performed for rainfall data. For rainfall of Bangladesh most of the stations, viz. Dhaka, Sylhet, Rangpur, Khulna showed significant upward trend. There were rising rates of rainfall in some months such as April in Rangpur and September in Khulna and a decreasing trend in some other months as in January in Sylhet were obtained by these statistical tests suggested overall significant changes in rainfall trend in these areas. Monthly rainfall and annual total rainfall were found to decrease at the rates of 4.94 mm/year and 16.11 mm/year, respectively, where the downward trend of monthly total rainfall was insignificant but the trend of annual total rainfall was significant with 5% level of significance.
 Ann. Bangladesh Agric. (2019) 23(1) : 49-61

Temporal Analysis of Daily and 10 Minutes of Rainfall of Poprad Station in Eastern Slovakia

The aim of this paper is the application of temporal analysis of daily and 10 min of rainfall data from Poprad station, located in Eastern Slovakia. There are two types of data used in the analysis, firstly, a daily time step data, manually collected between the years 1951 and 2018 and secondly, 10 min of data, automatically collected between the years 2000 and 2018. For proper comparability, the automatically collected data has been recalculated to the daily form. After a comparison of the sets of data, manually collected daily data has been used in further analysis. The main analysis can be divided into two sections. The first section consists of basic statistics (mean, standard deviation, etc.) and the second section of descriptive statistics, where the subjects of examination were trend, stationarity, homogeneity, periodicity and noise. The results of the basic statistics outlined trend behavior in the data meaning that the annual total rainfall for the period 1951–2018 is slightly increasing but the further investigation supported by the methods of descriptive statistics refuted this thesis. The number of rainy days is decreasing but maximum rainfall intensity is increasing year by year, indicating that total rainfall is happening in lesser and lesser days, with an increase in the number of 0 rainfall days. The results demonstrated no presence of the trend or only a weak trend in daily time step, but a significant increasing trend in annual rainfall. Tests of stationarity proved that the data are stationary and, therefore, suitable for any hydrologic analysis. The tests of homogeneity showed no breakpoints in the data. The interesting result was demonstrated by the periodicity test, which showed exactly a 365.25 days’ period, while 0.25 indicates a leap year. As a summary for the Poprad station, there is no tendency of increasing of daily average rainfall, but slight increasing trend of total annual rainfall, the summer season has the highest ratio on total precipitation per year, September and October are the months with the highest numbers of days without rain.

Trend analysis of rainfall, rainy days and drought: a case study of Ghataprabha River Basin, India

Drought is a recurring natural hazard, which has the potential to alter the ecological conditions of a region. A deficit in rainfall and a decrease in the number of rainy days induce the meteorological drought. The present study considered the nonparametric Mann–Kendall to investigate annual and seasonal rainfall (rainy-day) trend and meteorological drought trends over the Ghataprabha River Basin, India. A significant number of moderate and severe droughts were observed over the study period, and the eastern portion of the basin possessed the highest number of drought frequency (20–35 No.) in all the time scales of SPI. Results of trend analysis revealed that the stations having significant negative SPI trends are increasing with the SPI time scale, which could lead to the droughts of higher duration and severity. From the study, it was also noted that the negative trend of SPI was moving from the western portion of the basin to the eastern side, as the SPI time scale increases. Comparison between rainfall trend and rainy-day trend with SPI trend revealed high (ranging from 0.91 to 0.97) and moderate (0.67–0.7) correlation, respectively. This indicates that the rainfall trend will capture the SPI trends effectively. The findings of this work could be useful for a better understanding of regional drought trends and also establish effective water resources management policies over the basin.

Analysis of spatio-temporal climate variability of a shallow lake catchment in Tanzania

Abstract This study analyzed the trends and spatio-temporal variability in rainfall and temperature, and the length of the rainy season (LRS) in the Lake Manyara catchment, Tanzania, covering a period between 1988 and 2018 using stations and satellite climate product. The Mann-Kendall statistical test, Sen's slope estimator, and inverse distance weighting interpolation techniques were used to detect the trends, magnitude of trends and spatial distribution of rainfall and temperature. A modified Stern's method and water balance concept were used for rainfall onset, cessation and LRS analysis, while a standardized precipitation index (SPI) was used to investigate the wetness or dryness of the area. The results showed high variability and decreasing trend (4 mm/y) in annual rainfall, and non-significant increasing trend for minimum and maximum temperature. Rainfall increased from the western to the northern part of the catchment whereas a reversal pattern was noticed for temperature. The SPI shows a signal of normal condition (about 65%) for all stations – with few years showing evidence of wetter and drier conditions. The LRS showed a decreasing trend indicating a potential negative influence on rain-dependent activities. There is a need, therefore, for adaptation measures such as improving water productivity and irrigation at the farm and catchment level.

Trends and spatial patterns of 20th century temperature, rainfall and PET in the semi-arid Logone River basin, Sub-Saharan Africa

Sub-Saharan floodplains are sensitive to climatic changes in their upstream drainage basin, a major concern is given the dependency of millions of people for their daily subsistence. Understanding hydroclimatic trends and variability is critical for developing integrated coupled human and natural system models to evaluate future scenarios of vulnerability. Here we describe the historical climatic changes in the Logone River basin using grid-based climatic data during a time of concomitant human hydrological modification of the floodplain. Temporal trends were analysed by comparing two periods i.e. 1901/1921–1961 (pre-1960) and 1961–2013 (post-1960). Trends were analysed spatially based on the basin's two Köppen climatic zones: savanna (Aw) covering the southern upstream areas and semi-arid hot (BSh) covering the northern downstream areas. The results show significant increasing trends in maximum and minimum temperatures and potential evapotranspiration (PET), and non-significant decreasing trends in annual rainfall and number of rainy days, across the study area. These climatic changes on temporal and spatial scales play an important role for the coupled natural and human systems in the Logone floodplain.

Rainfall Trends in the North-Western and Eastern Coastal Lines of Sri Lanka Using Non – Parametric Analysis

The changes in the global rainfall have raised concerns over the present and possible future use of coastal areas in many Asian countries including Sri Lanka. However, no in-depth analysis of rainfall of these coastal lines of Sri Lanka has been performed yet to understand any changes in the pattern in general. This study was carried out to fulfil the above need, especially focusing on rainfall of North-Western and Eastern coastal lines of Sri Lanka. The rainfall data for a period of 30 years (1986–2016) were used in the study and analysis was performed using the tests, Mann Kendall, Sen’s slope estimator, and sequential Mann Kendall. Mann–Kendall’s test indicated positive trend in annual rainfall of most parts of North-Western coastal line but negative monotonic decrease at 4 stations, namely, Chilaw, Horakele, Lunuwila and Palaviya. In the Eastern coastal line, significant positive trend in annual rainfall was observed at 4 stations, namely, Kantale, Batticaloa, Pottuvil and Mylambaveli. The monthly rainfall analysis of North-Western coastal line revealed significant positive trends at Kottukachchiya and Anamaduwa stations in March and December respectively and in the Eastern costal line, positive trends were observed at Kantalae, Mylambaveli and Navatkiri Aru for February. The stations except Anamaduwa in NorthWestern coastal line recorded a significant negative trend in rainfall in the month of May. No station showed a significant positive trend during Southwest Monsoon season. During the Northeast Monsoon season, all the nineteen stations showed an increase in rainfall amounts while two locations in NorthWestern region and six locations in Eastern showed a significant upward trend. With these dynamic rainfall trends, it can be reiterated that it is vital to advocate climate mitigating actions to reduce impacts of changes in rainfall trends.

Drought Frequency, Severity, and Duration Monitoring Based on Climate Change in Southern and Southeastern Ethiopia

Ethiopia is highly vulnerable to the impact of climate change due to its low adaptive capacity and a higher dependence on rain-fed agriculture for livelihood. The aim of this paper was to identify the long-term climatic trends and the magnitude of those trends and to analyse drought duration, frequency, and severity in southern and south-eastern Ethiopia based on climatic data (1980-2017). This research is a quantitative research method. The southern and south-eastern of Ethiopia were purposely selected based on a frequent occurrence of drought in the country. Monthly data were obtained from National Meteorological Agency (NMA) of Ethiopia. Mann-Kendall (MK) Test coupled with Sen’s Slope Estimator was used to analyse the trend of climatic data and its magnitude, and Standardized Precipitation Evapotranspiration Index (SPEI) was used to analysis drought characteristics. SPEI of 1-, 3- and 6-month timescales were calculated to understand drought characteristics. The result of the MK test showed that annual rainfall trend had non-significant decrease at all station except at Gode. The trend of annual maximum and minimum temperature is insignificantly increasing. The calculated SPEI revealed drought is more frequent and severe from time to time in the study area. Results showed that the most frequent, severe and prolonged droughts occurred during1999-2017 compared to 1980-1999. Climate change mitigation and proactive drought management approach is highly recommended in order to minimize the risk of drought.

Crop planning strategies under changing rainfall scenario

An attempt has been made to study the impact of annual rainfall and its trend on crop production and productivity of different crops at Banka district of Bihar state by using 19 years rainfall data (2000-2018) and crop data for 21 years (1998-2017). In this district, rice is cultivated in 80% of area posing high risk of crop failure due to late onset and unusual behaviour of monsoon during kharif season. During rabi season, large area of the district is under wheat and low water demand crops like pulses and oilseeds cultivation. An average annual rainfall of 1063.1 mm was observed from 19 years rainfall data and a decreasing trend of annual rainfall was noticed in recent years. This changing rainfall pattern is the result of climate change and it responsible for drought like situation during monsoon month and heavy rainfall at crop maturity or harvesting stage which directly or indirectly damage the crop and its yield. The trend of area, production and productivity of major field crops (Rice, Wheat, Maize, Gram, Lentil and Rapeseed/Mustard) of Banka district was analysed for the period of 1998-2017. The results showed that there was a non-significant decreasing trend of acreage of all these crops were found mainly due to untimely and uneven distribution of rainfall. But a significant increasing trend of productivity was shown in all crops except rapeseed/mustard. The production trend of rice and maize crops are increasing with a significant value. From the analysis, it was concluded that the water requirement will increase in future. Therefore, it is suggested that water saving practices or techniques for water conservation and ground water recharge should be adopted over wide areas and short duration, drought resistant, less water loving crops or varieties need to be used in this district.

Recent Trend in Hydroclimatic Conditions in the Senegal River Basin

Analyzing trends of annual rainfall and assessing the impacts of these trends on the hydrological regime are crucial in the context of climate change and increasing water use. This research investigates the recent trend of hydroclimatic variables in the Senegal River basin based on 36 rain gauge stations and three hydrometric stations not influenced by hydraulic structures. The Man Kendall and Pettitt’s tests were applied for the annual rainfall time series from 1940 to 2013 to detect the shift and the general trend of the annual rainfall. In addition, trends of average annual flow rate (AAFR), maximum daily flow (MADF), and low flow rate (LFR) were evaluated before and after annual rainfall shift. The results show that the first shift is situated on average at 1969 whereas the second one is at 1994. While the first shift is very consistent between stations (between 1966 and 1972), there is a significant dispersion of the second change-point between 1984 and 2002. After the second shift (1994), an increase of annual rainfall is noticed compared to the previous period (1969–1994) which indicates a not significant, partial rainfall recovery at the basin level. The relative changes of hydrologic variables differ based on the variables and the sub-basin. Relative changes before and after first change-point are significantly negative for all variables. The highest relative changes are observed for the AAFR. Considering the periods before and second shifts, the relative changes are mainly significantly positive except for the LFR.

Impacts of Triple Factors on Flash Flood Vulnerability in Egypt: Urban Growth, Extreme Climate, and Mismanagement

Urban growth, extreme climate, and mismanagement are crucial controlling factors that affect flood vulnerability at wadi catchments. Therefore, this study attempts to understand the impacts of these three factors on the flash flood vulnerability in different climatic regions in Egypt. An integrated approach is presented to evaluate the urban growth from 1984 to 2019 by using Google Images and SENTINEL-2 data, and to develop hazard maps by using a rainfall-runoff-inundation model (RRI). Annual rainfall trend analysis was performed to evaluate the temporal variability trend. The hazard maps that were created were classified into three categories (low, medium, and high) and integrated with the urban growth maps to evaluate the impacts on the flood-vulnerable areas. The results show a significant increase in urban growth resulting in an increase of prone areas for flood hazards over time. However, the degree of this hazard is mainly related to growth directions. Mismanagement affects urban growth directions in both planned and unplanned growth, whether by loss of control over unplanned growth or by deficiencies in approved plans. The rainfall analysis showed that there is no explicit relationship to increases or decreases in the flood vulnerable areas. An urban planning approach is recommended for risk reduction management based on a comprehensive study considering such factors.

Trends of rainfall and rainy days at Sindewahi station in Vidarbha of Maharashtra

Changes in climate over the Indian region would have significant impact on agricultural production, water resources management and overall economy of the country. This study focuses on Rainfall variation and detecting trends in the annual, monthly, seasonal and weekly rainfall and rainy days for Sindewahi station in Chandrapur District (eastern part) in Vidarbha Region of Maharashtra State. The analysis of rainfall variation was done by using statistical parametric test and trend analysis was done by using Mann-Kendall and Sen’s slope test. The results revealed that no trend in annual and seasonal rainfall and rainy days whereas rising trend of rainfall observed in September months at 90 per cent confidence level. In rainfall and rainy days SMW 22 and SMW 30, 38 showed decreasing and increasing trend respectively. There are rising rates of rainfall and rainy days in other months and decreasing trend in some other months obtained at non-significant condition by these statistical tests suggesting overall insignificant changes in the area. The decreasing trend in rainfall, rainy days creating the moisture deficiency during crop growing period which ultimately is losing the productivity in rainfed agriculture. To mitigate the adverse effect of uncertainty of rainfall, it is proposed to adopt the location specific in situ soil and moisture conservation practices before and after commencement of the rains and to harvest the excess runoff into farm ponds and recycled for providing protective irrigation for sustainable rainfed agriculture.

Long-term trend analysis of climate variables for arid and semi-arid regions of an Indian State Rajasthan

Variations of rainfall as well as temperature for long term are one of the elements in variability of climate. In this paper, trend detection has been studied for the period of rainfall data from year 1871 to 2016 and temperature data from 1901 to 2002 for the entire state. To detect the existing trend, Mann-Kendall test is performed and to detect the magnitude of trend, Sens slope estimator tests were performed. Trend analysis of rainfall over 146 years shows increasing trend in pre monsoon, southwest monsoon and annual precipitation in west Rajasthan while the result shows increasing trend in pre monsoon, post monsoon and annual rainfall in the east Rajasthan. Trend analysis of temperature over 102 years shows increasing trend in annual temperature in both regions. It can be concluded that there are significant changes in the trend of rainfall and temperature of the region. This study would be useful to hydrologists, water resource engineers, researchers and consultants dealing with the impact of climate change for sustainable development and water resource planning.

Assessment of seasonal and annual rainfall trend in Calabria (southern Italy) with the ITA method

Abstract In this paper, an investigation on the temporal variability of seasonal and annual rainfall in the Calabria region (southern Italy) was carried out using a homogeneous and gap-filled monthly rainfall dataset of 129 rain gauges in the period 1951–2006. In particular, possible trends have been assessed by means of the Innovative Trend Analysis (ITA) technique, which allows the identification of a trend in the low, medium and high values of a series. Moreover, the results obtained with the ITA have been compared with the ones obtained with the Mann–Kendall test. These analyses have been performed in five rainfall zones (RZs) of the study area, characterized by different climatic conditions. As a result, both the methods evidenced a negative trend of the annual rainfall in the entire study area. On a seasonal scale, this negative tendency has been confirmed in autumn and winter although with some differences among the several RZs.

Recent rainfall trend over Sri Lanka (1987–2017)

AbstractRainfall trend analysis provides useful information for effective planning, and management of water resources, and gives an insight into climate change of a region. This study investigates trends in annual and seasonal rainfall over Sri Lanka using an Innovative Trend Analysis (ITA) and Mann–Kendall (MK) test with Sen's slope estimator. The MK test showed increasing trends in annual rainfall at 24 stations (65%) with five stations showing significant increasing trend. Annual rainfall at 13 locations (35%) showed decreasing trend, but none were significant (p < .05). ITA results for annual rainfall showed increasing trend at 67% stations while 33% stations showed decreasing trend. MK test results for seasonal rainfall indicated increasing trend at 76, 51, 32, and 86% of stations during First Inter‐Monsoon (FIM), Second Inter‐Monsoon (SIM), South West Monsoon (SWM), and North East Monsoon (NEM) seasons, respectively. Seasonal analysis of rainfall trend using ITA method showed increasing trend in 81, 70, 32, and 65% stations during FIM, SIM, SWM, and NEM, respectively. ITA and MK tests exhibited similar trend results for 80% of the stations. Moreover, Spearman's rho correlation coefficient between ITA and MK test trends showed significant (p < .05) positive correlation. In general, eastern, south eastern, north and north central regions of the country showed increasing rainfall trend over the last 31 years (1987–2017) while western, part of north western and central part of the country indicated a decreasing rainfall trend during the same period.

Spatial and temporal climate variability and change in the bilate catchment, central Rift Valley lakes region, Ethiopia

ABSTRACT The paper explores spatial and temporal variability of rainfall and temperature in Bilate catchment based on monthly data of 11 meteorological stations. Precipitation Concentration Index (PCI) and Pearson product moment correlation were used to estimate monthly concentrations and associations between annual and seasonal rainfall. Similar methods were used to analyze the association of ENSO with rainfall variability using Eastern Equatorial Pacific (Niño 3.4) data, Sea Surface Temperature (SST), and Southern Oscillation Index (SOI). Rainfall and temperature series were tested for trends using the Mann–Kendall test. Rainfall in the catchment is highly seasonal and concentrated in Kiremt (June–September), followed by Belg (February–May). Belg rainfall was highly variable. Annual rainfall was relatively stable in the upper catchment and variable in the lower catchment. PCI values are expected to increase as annual and seasonal rainfall decrease. The middle catchment had significant negative trends in annual and Belg rainfall. November–March SST is strongly associated with Belg rainfall variations throughout the catchment, and ~49% of the variability can be explained by Equatorial Pacific SST. Annual and seasonal temperature significantly increased in middle and lower parts of the catchment in the past 30 years. Warming was ~0.05°C/yr to 0.17°C/yr.

Management of drought in sali rice under increasing rainfall variability in the North Bank Plains Zone of Assam, North East India

The intermittent dry spells during growing season of winter or sali rice, cultivated in NBPZ of Assam located in the foothills of Eastern Himalayan region, is a major weather risk causing widespread damage to the crop. Herein, variability of rainfall in Lakhimpur district situated in NBPZ was studied. A significant decreasing trend of annual and seasonal rainfall was observed. Significant decrease in monsoon rainfall and increase in monthly rainfall variability clearly explains the recent rainfall fluctuations with increasing frequency of intermittent dry spells and flash floods. A participatory evaluation trial was conducted in Chamua village of Lakhimpur district having different land situations to identify climate resilient technologies to cope with seasonal drought in sali rice. High-yielding short-duration varieties, viz., Dishang, Luit, Lachit and Kolong, and medium-duration varieties, viz., Basundhara, Mohan, Mulagabhoru and TTB-404 performed consistently better than the long-duration HYV or the traditional varieties under upland and medium land situations, respectively. Though the effect of dry spells on long-duration varieties cultivated on low lands was least, yield of these varieties reduced up to 43.07% when sowing was delayed beyond 23rd of June. Performance of the delayed sown varieties was further declined, when exposed to dry spells at later growth stages. However, adverse impact of dry spells can be managed effectively by replacing farmers’ varieties with short and medium-duration high-yielding varieties in upland and medium lands, respectively, and manipulating sowing time of long-duration varieties for low lands.

Long-term rainfall characteristics in the Mzingwane catchment of south-western Zimbabwe

Rainfall characteristics during the annual rainy season are explored for the Mzingwane catchment of south-western Zimbabwe, for both historic period (1886–1906) and more recent times (1950–2015), based on available daily and monthly precipitation series. Annual and seasonal rainfall trends are determined using the modified Mann-Kendall test, magnitude of trends test and Sen’s slope estimator. Rainfall variability is quantified using the coefficient of variation (CV), precipitation concentration index (PCI) and standard precipitation index (SPI). Results suggest that contemporary mean annual rainfall may not have changed from that measured during the historic period of 1886–1906. However, the number of rainy days (≥ 1 mm) has decreased by 34%, thus suggesting much more concentrated and increased rainfall intensity. A notable shift in both the onset and cessation dates of the rainy season is recorded, particularly during the twenty-first century, which has resulted in a significantly reduced (p < 0.05) length of the rainy season. The combination of a reduced number of rainy days (≥ 1 mm) and a shortened rainy season suggests that long intra-season dry spells have become more common through time and have considerable negative consequences for agriculture and wetland ecosystem in the region. In addition, high spatio-temporal rainfall variability and seasonal PCI values indicate strong seasonality in the rainy season. Based on the SPI results, the El Nino Southern Oscillation (ENSO) strongly influences rainfall variability. The results further suggest high uncertainty in rain season characteristics, which requires effective planning for water needs.

Analysis of Runoff and Sediment Yield Characteristics in Small Watershed of Taihang Mountain Area

With the small watershed of Chongling in the Taihang Mountain area as the study area, and with the experimental data of the watershed test base collected for years, this paper studies the characteristics of rainfall, runoff and sediment yield of this area. The results show that the adequacy and inadequacy of rainfall in the study area was alternate from 1959 to 2017, and the interannual changes were large, showing non-significant trend of annual rainfall. Vegetation cover can retain surface runoff. When the rainfall was below 250mm in August, the runoff after afforestation was significantly reduced. When the rainfall was over 250mm in August, the runoff quantity changes before and after afforestation were not significant.

Impact of climate change on the rainfall pattern of Klip River catchment in Ladysmith, KwaZulu Natal, South Africa

Rainfall trend analysis has been of major focus in the past century because of the attention given to climate change by the science and engineering community. According to some latest studies, rainfall is one of the main parameters in any catchment which plays a significant role in flood frequency, flood control as well as water resources planning and management. Ladysmith town in South Africa is flooded almost every year resulting in loss of lives as well as properties and businesses. Thus, this study aimed at determining the monthly and annual rainfall pattern in relation to climate change. The monthly, seasonal and annual rainfall trends for the period 1985 – 2018 were analyzed using Mann-Kendall test and Sen’s slope estimation. Results of this study indicated a variability in seasonal rainfall, with a rainfall increase during December and January of summer months whose Mann-Kendall test results were 1.88 and 0.73, and a major decrease showed in autumn months (March, April, and May) with Mann-Kendall test values of -2.76, -3.53 and -4.09. Thus, the overall results suggest a minor significant change for both Ladysmith and upstream of the Klip river catchment. Based on the analysis, it can be concluded that climate change has an impact on the rainfall spatial pattern of the study area. This correlates well with similar analysis carried out in other areas around the world.