Rainfall Trend Analysis Research Articles

Spatial-temporal trend analysis of seasonal and annual rainfall (1966–2015) using innovative trend analysis method with significance test

This study investigates the spatial and temporal patterns of trends on seasonal (pre-monsoon, monsoon, post-monsoon, and winter) and annual rainfall time series data (1966–2015) at 13 stations located in the central Himalayan region of the Uttarakhand State of India. The temporal trend was analyzed using recently proposed innovative trend analysis (ITA) method with significance test. The results of the ITA method were compared with the Mann-Kendall (MK) test at 5% significance level. The spatial variation of the trends in seasonal and annual rainfall series was interpolated using the Thiessen polygon (TP) method in ArcGIS 10.2 environment. The results of comparison revealed that the trend detected by MK test (significantly positive in 3-time series and significantly negative in 6-time series) can be effectively identified using ITA (significantly positive in 19-time series and significantly negative in 32-time series). The ITA method could detect some trends that cannot be observed by the MK test. According to the spatial distribution of MK test, significantly increasing (decreasing) trends were observed in 1 (0), 1 (2), 0 (1), 1 (1), and 1 (1) polygons in pre-monsoon, monsoon, post-monsoon, winter, and annual rainfall data, while the ITA method detected significant trends in 3 (7), 6 (5), 1 (9), 4 (5), and 5 (6) polygons in the study region. The developed maps of spatial variability of rainfall trends may help the stakeholders and/or water resource managers to figure out the risk and vulnerability related to climate change in the study region.

Impact of climate variability on hydropower generation in an un-gauged catchment: Erathna run-of-the-river hydropower plant, Sri Lanka

Impact of climate change or climate variability on water resources is an exceedingly concerned issue. Hydropower development is one of the most affected industries due to the climatic variability. Therefore, this paper presents the promising results from a study of the impact of climate variability on hydropower generation of Erathna run-of-the-river (ROR) hydropower plant located in Rathnapura district, Sri Lanka. This study was based on surrounded rain gauges outside the catchment as Erathna catchment area is an un-gauged catchment. 30-year rainfall trend analysis from 1988 to 2017 was done using Mann–Kendall and Sen’s slope estimator tests to predict the available trends. Pearson’s correlation coefficient was used to investigate the relationship between rainfall and Erathna power generation. Results show negative trends for annual rainfalls in several rain gauges, while seasonal trend analyses support that observation. July is the most critical month for most of the rain gauges around the catchment. The results also show a good correlation between the rainfalls and power generation. Therefore, the results conclude the importance of rainfall trend analysis in un-gauged catchments and its forecasting capacity of water resources usage in hydropower development.

An analysis of extreme rainfall trends from 1960 to 2015 in urban areas of Surabaya

Extreme rainfall event considered as the primary cause of many hydro-meteorological disasters around the world. Extreme rainfall event propagated more prolonged disaster when occurring in urbanised areas. This research presents an analysis of trend and rainfall variability in the most urbanised areas of East Java. The study is conducted at Surabaya City and its sub-urban areas (Mojokerto, Sidoarjo). Daily rainfall data from 1960 to 2015 obtained from existing measurement sites are used as input for this study. Firstly, a frequency distribution of extreme rainfalls (1-day maximum) is presented. Then, analysis of trend detection conducted using Mann-Kendall, Rank-Sum and Median Crossing test. Finally, spatial variability of extreme rainfall was presented by interpolating point measurement to produce thematics maps. The interpolation was conducted using IDW methods. The results show the trend and variability (temporal and spatial) of extreme rainfalls on the regions of Surabaya.

Assessment of the Effects of Flood on Agricultural Land Use in Doma Local Government Area, Nasarawa State, Nigeria

This study aimed at assessing the effects of flood on agricultural land use in Doma Local Government Area, Nasarawa state, Nigeria. In order to achieve the objectives of the study, information on the causes effects frequency and magnitude of flood on agricultural land use were needed from primary and secondary source of data. The primary data were obtained through the use of structured questionnaire, field observation and measurement and ten years rainfall data (2004-2014). The rainfall data were obtained from Nigeria meteorological agency (NIMET), Lafia, Nasarawa state. Rainfall data obtained were used for rainfall trend analysis for the study. The secondary data include information from relevant text such as journals, newspaper dictionary, encyclopaedia textbooks, internet and web and related past students dissertation and thesis. Basic statistical techniques such as the computation of totals, mean, and standard deviation were employed for the analysis of rainfall data. Descriptive statistics were adopted to analyze the result from the questionnaire and simply linear regression analysis were used to determined rainfall trend for this work. The study shows that there has an appreciable effect of flood in the study area which is due to many factors such as human activities but is greatly influenced by climate. This evident in the study as about 44.1% and 21.8% of the total respondents have been engaged in farming for 21 years and above, and 16 to 20 years respectively and are thereby able to explain clearly the effects they home observed experienced over time. The finding also revealed that 1.76% of the respondents have lost a total 15 hectares of farm land, 30.59% have 416 hectare 23.53 have lost 480 hectares, 14.71% lost 500 histories and 7.06% 600 hectares respective. This indicates a great destruction farm lands in the area and invariably a decrease in food production. The state disaster management and other agencies charges with disaster management in the state level should be properly funded in order to respond to the challenges of sudden of occurrences of natural disaster in future. Keywords: Effect, Floods, Agriculture, Landuse, Devastation DOI : 10.7176/JEES/9-3-08 Publication date :March 31 st 2019

Rainfall Trend Analysis in Context of Climate Change in Guercif City, Morocco

The purpose of this study is to analyze the variations of rainfall events through a statistical analysis of rainfall data in Guercif station for a period of 45 years (1971-2015). The analysis of rainfall trends in Guercif station showed that global warming which we are so concerned about seem to have resulted in an increase in rainfall and not drought. Moreover, the Gumbel method has allowed us to determine return periods of rainfall. The results have shown that the rainfall is low. The annual rainfall reaches a maximum of 359 mm with a 100 year return period.

Rainfall Trend Analysis in the City of Villahermosa, Mexico

Rainfall Trend Analysis in the City of Villahermosa, Mexico

Trend analysis of rainfall and drought over the Oum Er-Rbia River Basin in Morocco during 1970–2010

In a context of water scarcity in Morocco, the proper management of water resources is becoming a national priority. However, the strong spatiotemporal fluctuation of rainfall, considered as the first source of surface water intakes, complicates attempts to work on such a long-term purpose. In this work, we aim to provide an analysis of rainfall variability over the Oum Er-Rbia (OER) River basin, one of the most important basins in Morocco. For this, we assessed the annual rainfall deficit using the Standardized Precipitation Index (SPI) and then analyzed trends at annual, seasonal, and monthly bases using the Mann–Kendall test. The study was conducted on a set of data from 15 stations over a 40-years period (1970–2010). The results show that the OER River basin tends towards drier conditions. An abundance of deficit seasons has been noticed (50 to 63% of the seasons), especially after 1980–1981. Since then, the basin has known several deficit periods, sometimes of great spatial extent such as those that occurred in the 1980s and 1990s. Moreover, during the study period, the total annual rainfall has demonstrated a general decreasing tendency. The latter was mainly induced by changes in winter and spring months, which experienced some of the largest decline rates with a special abundant significance during the month of April.

Regional scale analysis of trends in rainfall using nonparametric methods and wavelet transforms over a semi‐arid region in India

Space‐time variability of rainfall at local scale is affected by several regional factors such as aerosol concentration, greenhouse gases, land cover changes, etc., along with large scale atmospheric circulations. Predictive ability of regional circulation models can be significantly improved and efficient management of water resources can be assured by identifying dominant variables controlling spatiotemporal variations in rainfall among aforementioned factors. The present study aims to investigate dominant climate system(s) controlling trends in rainfall over Chhattisgarh state (a semi‐arid region) in India over the period of 115 years (1901–2015). Discrete wavelet transform in conjunction with Mann–Kendall test is applied to the rainfall data series at different time scales (monthly, seasonal, annual, pre‐monsoon, monsoon, post‐monsoon and winter) in order to identify the long term trends and dominant periodic components influencing the trend. In the results, negative trends are found to exist in all rainfall time series at majority of districts (except for annual and monsoon rainfall at Bijapur and Sukma district). In addition, analysis of trend in actual evapotranspiration and soil moisture in the region does not exhibits the effect of anthropogenic variables (such as land cover change, irrigation projects, etc.) on the rainfall as significant negative trend are also observed in soil moisture for majority of districts. Overall, 2‐year and 4‐year periodic components have been detected to be dominating the trends in most of the rainfall time series (annual, monsoon, post‐monsoon and winter). On comparing the identified dominating components with the existing climate systems (Atlantic multidecadal oscillations, Indian ocean dipole, Madden‐Julian oscillations, Inter‐Tropical Convergence Zone, etc.), El Niño‐Southern Oscillations has been recognized as predominant climate circulation influencing the rainfall trends over the study region. The study outcomes are expected to improve the regional precipitation forecasts and should be useful in various hydro‐meteorological analyses and decision making at regional scale.

Rainfall trend analysis and future scenario assessment by using mathematical and statistical techniques for South Gujarat

In the present study, attempts have been made to study temporal variation in seasonal and annual rainfall over the two districts of South Gujarat during the period 1901 to 2012. The statistical and mathematical analysis of annual rainfall indicates good range of variation of Navsari and Bharuch region for 112 years (1901 to 2012) period. The mean, median, mode, standard deviation, coefficient of dispersion, coefficient of variation and coefficient of skewness of Navsari was found 1515.5 mm, 1430.0 mm, 1444.2 mm, 481.4 mm, 0.318 mm, 31.8%, 0.148 mm and for Bharuch the values were found 972.0 mm, 959.5 mm, 913.7 mm, 293.3 mm, 0.302 mm, 30.2% and 0.199 mm respectively. The annual rainfall over Navsari showed a long term increasing trend, an increase of 304.64 mm only was noticed during the study period of 112 years as against the normal rainfall of 1517.90 mm. Similarly, for Bharuch a decrease of 39.98 mm only was noticed during the study period of 112 years as against the normal rainfall of 972.10 mm. Mode analysis shows class interval 1400 to 1599 has highest number of frequencies of rainfall (21) in Navsari region and for Bharuch highest number of frequencies (32) was found under interval 800 to 999.

Analysis of Average Annual Rainfall and Average Maximum Annual Temperature for a Period of 30 years to Establish Trends in Kieni, Central Kenya

Analysis of Average Annual Rainfall and Average Maximum Annual Temperature for a Period of 30 years to Establish Trends in Kieni, Central Kenya

Change in Climate Extremes and Pan Evaporation Influencing Factors over Ouémé Delta in Bénin

This work focuses on trend analysis of rainfall, evaporation, temperature, relative humidity, wind speed, and sunshine duration over the Ouémé Delta in Bénin. Eight temperature based indices and fifteen rainfall based indices are computed from 1960 to 2016. Moreover, maximum 1, 2, 3, 5, and 10 days precipitation indices were computed at the monthly scale. Trends are detected at 0.05 confidence level, using a combination of Mann-Kendall and prewhitened Mann-Kendall test. Partial correlation and stepwise regression are used to detect the set of meteorological variables that influence pan evaporation in Ouémé Delta. Results showed intensification of heavy rainfall over Ouémé Delta. Moreover, a significant increasing trend is detected in temperature. As consequence, diurnal temperature significantly decreases as proof of the global warming. Average pan evaporation showed a significant slither increasing trend over the area. Change in pan evaporation can be explained by wind speed and sunshine duration that hold almost 50% of pan evaporation variance. As future temperature is going to be increasing, pan evaporation may increase considerably. So, adaptation measures have to be reinforced in the Ouémé Delta area where farmer are used to rainfed agriculture for food security. Moreover, Ouémé Delta plan have to be developed for it resources sustainability.

Analysis of Rainfall and Temperature Trends in Bahati Sub-County, Kenya

This study analyzed the climate variability trends in Bahati Sub-County, Kenya for the period 1985 to 2015.The climate parameters used included rainfall onset, rainfall cessations, seasonal rain, annual rainfall, annual mean temperature, maximum and minimum temperature. Data on rainfall and temperature was collected from Nakuru Meteorological Station. The strength and direction of the relationship between rainfall and temperature was determined using SPSS software version 23 (correlation analysis) and Microsoft Office Excel 2010 to generate frequency tables, pie charts, graphs and moving averages. The findings revealed that there is a significant, negative and strong relationship between annual rainfall trend and maximum temperature (r= -0.716, p = 0.000). However, the study findings also revealed that the relationship between annual rainfall and minimum temperature had an insignificant, weak and negative relationship (r= 0.151, p= 0.418).

Spatio-Temporal Trend Analysis of Rainfall and Temperature Extremes in the Vea Catchment, Ghana

This study examined the trends in annual rainfall and temperature extremes over the Vea catchment for the period 1985–2016, using quality-controlled stations and a high resolution (5 km) Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) data. The CHIRPS gridded precipitation data’s ability in reproducing the climatology of the catchment was evaluated. The extreme rainfall and temperature indices were computed using a RClimdex package by considering seventeen (17) climate change indices from the Expert Team on Climate Change Detection Monitoring Indices (ETCCDMI). Trend detection and quantification in the rainfall (frequency and intensity) and temperature extreme indices were analyzed using the non-parametric Mann–Kendall (MK) test and Sen’s slope estimator. The results show a very high seasonal correlation coefficient (r = 0.99), Nash–Sutcliff efficiency (0.98) and percentage bias (4.4% and −8.1%) between the stations and the gridded data. An investigation of dry and wet years using Standardized Anomaly Index shows 45.5% frequency of drier than normal periods compared to 54.5% wetter than normal periods in the catchment with 1999 and 2003 been extremely wet years while the year 1990 and 2013 were extremely dry. The intensity and magnitude of extreme rainfall indices show a decreasing trend for more than 78% of the rainfall locations while positive trends were observed in the frequency of extreme rainfall indices (R10mm, R20mm, and CDD) with the exception of consecutive wet days (CWD) that shows a decreasing trend. A general warming trend over the catchment was observed through the increase in the annual number of warm days (TX90p), warm nights (TN90p) and warm spells (WSDI). The spatial distribution analysis shows a high frequency and intensity of extremes rainfall indices in the south of the catchment compared to the middle and northern of part of the catchment, while temperature extremes were uniformly distributed over the catchment.

Analysis of trends in rainfall and dry/wet years over a century in the Eastern Ganga Canal command

In the present study, an attempt has been made to analyse the variability and trends in annual and seasonal rainfall over the Eastern Ganga Canal command area, India. To determine the trend in annual/seasonal rainfall and rainy days, the non‐parametric Mann−Kendall test and Sen's slope method were used over daily gridded rainfall for the time period 1901–2012. The results of the trend analysis revealed a decreasing trend in annual and monsoon rainfall in the range 18.5−61.7 and 19.4−56.7 mm/decade, respectively. For annual and monsoon rainy days, the results demonstrated a decreasing trend which varied from 1.8 to 2.9 and 1.4 to 2.2 days/decade, respectively, and an increasing trend in the range 0.2−1.4 and 1.0 days/decade, respectively. A variability analysis was performed to highlight the need for selecting an appropriate confidence level in trend analysis. It was observed that the grids showing a statistically non‐significant trend at the 95% confidence level exhibit a statistically significant trend at lower confidence levels. An analysis of dry and wet years on an annual scale revealed that the chances of occurrence of a wet year are more in comparison with the chances of occurrence of a dry year in the command area by a ratio of 14:13. However, data from the last one and a half decades has a contradictory trend with higher chances of occurrence of a dry year to very minimal chances of occurrence of a wet year. Dependable rainfall at various probability levels was estimated using a gamma distribution function. It was observed that the 75% dependable weighted annual and seasonal rainfall over the command area (985.48 and 727.54 mm) was significantly different with respect to the climatic mean weighted annual and seasonal rainfall against the weighted mean annual and seasonal rainfall (1,165.93 and 901.95 mm).

Analysis of seasonal and annual rainfall trends for Ranchi district, Jharkhand, India

The aim of this study was to investigate temporal variation in seasonal and annual rainfall trend over Ranchi district of Jharkhand, India for the period (1901–2014: 113 years). Mean monthly rainfall data series were used to determine the significance and magnitude of the trend using non-parametric Mann–Kendall and Sen’s slope estimator. The analysis showed a significant decreased in rainfall during annual, winter and southwest monsoon rainfall while increased in pre-monsoon and post-monsoon rainfall over the Ranchi district. A positive trend is detected in pre-monsoon and post-monsoon rainfall data series while annual, winter and southwest monsoon rainfall showed a negative trend. The maximum decrease in rainfall was found for monsoon (− 1.348 mm year−1) and minimum (− 0.098 mm year−1) during winter rainfall. The trend of post-monsoon rainfall was found upward (0.068 mm year−1). The positive and negative trends of annual and seasonal rainfall were found statistically non-significant except monsoon rainfall at 5% level of significance. Rainfall variability pattern was calculated using coefficient of variation CV, %. Post-monsoon rainfall showed the maximum value of CV (70.80%), whereas annual rainfall exhibited the minimum value of CV (17.09%), respectively. In general, high variation of CV was found which showed that the entire region is very vulnerable to droughts and floods.

Rainfall trend analysis for crop planning under rainfed conditions in district Agra of Uttar Pradesh

Rainfall trend analysis for crop planning under rainfed conditions in district Agra of Uttar Pradesh

Analysis of rainfall trend and variability in Ebonyi state, South Eastern Nigeria

Analysis of rainfall trend and variability in Ebonyi state, South Eastern Nigeria

Analysis of Rainfall Trends and its Spatial Patterns During the Last Century over the Gangetic West Bengal, Eastern India

Long-term spatial and temporal trends of rainfall at monthly, seasonal, and annual scales have been studied for 12 meteorological stations of the Gangetic West Bengal located in Eastern India during 1901–2002 using 102 years of rainfall data. The non-parametric Mann-Kendall test and Sen’s slope estimator were used to detect trends and their slope. The changes are calculated in percentage over the time period. The results highlight a marked increase in post-monsoon (33.87%), the overall increase in annual (2.61%), a considerable decrease in winter (14.83%) as well as pre-monsoon (4.03%), and an inconsequential increase in monsoonal (1.21%) rainfall. In the annual and monsoonal series, the trend is positive in the southern half but negative in the northern counterpart. A considerable decrease in rainfall during June and August at most stations signifies that monsoon is losing in the early monsoonal months with an occurrence of mid-season dry spells. The increase in rainfall during September (13.80%) and October (34.38%) reveals that the monsoon is shifting toward these late monsoon and post-monsoon months, respectively. Both the decrease of rainfall in June (early monsoonal month), as well as an increase in rainfall in September (late monsoonal month) and October (start of post-monsoonal month), suggest that the monsoon is being delayed on its onset and withdrawal. In the Rarh region, monsoon rainfall is reducing whereas post-monsoon rainfall is increasing. In the Deltaic region, both monsoon and post-monsoon rainfalls are increasing. Such altering patterns of rainfall call for reviewing the agricultural practices and water use in this region.

Impact of Extreme Weather Events on Wheat Yield in Different Agro-Ecological Zones of Middle Indo-Gangetic Plain

The long period meteorological data of maximum temperature, minimum temperature and rainfall of Pusa, Purnia, Sabour and Patna stations representing different agro-ecological zone of middle Indo-Gangetic plain for the period (44–58 years) were analysed for trend analysis of temperature and rainfall for rabi season and heat waves, cold waves and extreme rainfall events for the whole year. The Theil–Sen’s slope and Mann–Kendall test were used to investigate the trends in climate variability (maximum and minimum temperature, rainfall) and extreme weather events (heat waves, cold waves and extreme rainfall). The maximum temperature had significant decreasing trend in Rabi season at Sabour. The minimum temperature had a significant increasing trend at all the stations in Rabi season. At Pusa, rainfall had a significant decreasing trend. Significant decreasing trend in heat waves at Pusa and Sabour stations were found. In this study, an attempt was made to assess the impact of these parameters on the productivity of wheat crop in Bihar. For this purpose, CROPSIM-Wheat model 4.6 was used to assess the change in wheat yield under different climate change scenarios for four locations viz. Pusa (zone I), Purnia (zone II), Sabour (zone III A) and Patna (zone III B) in Bihar. The model was run for the scenarios like increase in maximum temperature and minimum temperature with 1 °C, 2 °C and 3 °C separately and 1 °C, 2 °C, 3 °C, 4 °C increase in mean temperature keeping all parameters normal on wheat yield. Simulated wheat productivity revealed the reduction in grain yield by 7.4–10.4%, 15.3–21.2%, 21.6–30.9% and 26.9–38.6% in response to temperature rise by 1 °C, 2 °C, 3 °C and 4 °C, respectively, from baseline yield (1980–2010) at different locations. Warming temperature and greater incidence and intensity of extreme weather events due to climate change may significantly affect crop yield.

Analysis of rainfall trends of two complex mountain river basins on the southern slopes of the Central Himalayas

Understanding rainfall characteristics plays a vital role in sustainable watershed development and management, but at the same time it is challenging in mountainous regions, due to its topography complexities. This study investigates the seasonal along its associated months and annual rainfall characteristics and their variations over two distinct river basins; Kaligandaki in central west and Koshi in eastern Nepal, located on the southern slopes of the central Himalayas, which is crucial to the research of the climate change in these regions. The rainfall data series over the period of 34-year (1981–2015) of 43 stations between the elevation range of 143 m asl to 3870 m asl was used for this study. The analysis was carried out to assess the significance of rainfall trend along with its magnitude followed by its abrupt shift by using the Mann-Kendall test, Sen's test and Sequential Mann-Kendall test respectively. Furthermore, multitaper method was used to confirm the influence of large-scale circulation indices over the study area. An increasing pattern of rainfall from south to north was observed throughout all season in Koshi basin which was not seen in the Kaligandaki basin, indicating the effects of orography along with monsoon. Both basins share a similar pattern of rainfall between annual and monsoonal rainfall, supporting that both basins are dominated by the monsoon. The transition months between the seasons showed almost similar spatial distribution but different from other months of respective seasons. The results showed that the seasonal and annual rainfall declined in most of the stations of both the basins, except during pre-monsoon where it showed increased rainfall. But only a few stations showing such changes were statistically significant. In fact, these noticeable significant decreases were observed especially in the southern and northern region of Koshi basin while in Kaligandaki basin, it was found either in central or in the southern region. Furthermore, the trend shift analysis identified change points during 1980s or early 1990s, but most significant shifts were observed in recent years with some exceptions. Spectral analysis showed significant peaks at periodicity ranging 2–5 years, suggesting a potential association with Quasi-Biennial Oscillations (QBO) and El Niño-Southern Oscillation (ENSO).