Spatiotemporal variability of annual and seasonal rainfall time series in Ho Chi Minh city, Vietnam

2018 ◽  
Vol 10 (3) ◽  
pp. 658-670 ◽  
Author(s):  
Dang Nguyen Dong Phuong ◽  
Vu Thuy Linh ◽  
Tran Thong Nhat ◽  
Ho Minh Dung ◽  
Nguyen Kim Loi
Keyword(s):  
Time Series ◽  
Rainy Season ◽  
Kendall Test ◽  
Dry Season ◽  
Seasonal Rainfall ◽  
Spatiotemporal Variability ◽  
Ho Chi Minh City ◽  
Annual Rainfall ◽  
Rainfall Time Series ◽  
Spatial And Temporal Patterns

Abstract This study analyzed spatial and temporal patterns of rainfall time series from 14 proportionally distributed stations in Ho Chi Minh City for the period 1980–2016. Both parametric and nonparametric approaches, specifically, linear regression, the Mann–Kendall test and Sen's slope estimator, were applied to detect and estimate the annual and seasonal trends after using original and notched boxplots for the preliminary interpretation. The outcomes showed high domination of positive trends in the annual and seasonal rainfall time series over the 37-year period, but most statistically significant trends were observed in the dry season. The results of trend estimation also indicated higher increasing rates of rainfall in the dry season compared to the rainy season at most stations. Even though the total amount of annual rainfall is mainly contributed by rainfall during the rainy season, the pronounced increment in the dry season can be a determining factor of possible changes in annual rainfall. Additionally, the interpolated results revealed a consistently increasing trend in the southeastern parts of the study area (i.e., Can Gio district), where annual rainfall was by far the lowest intensity compared to other regions.

scholarly journals Investigating changes over time of annual rainfall in Zimbabwe

2010 ◽  
Vol 14 (12) ◽  
pp. 2671-2679 ◽  
Author(s):  
D. Mazvimavi
Keyword(s):  
Time Series ◽  
Regression Analysis ◽  
Quantile Regression ◽  
Rainy Season ◽  
Annual Rainfall ◽  
Rainfall Time Series ◽  
Average Rainfall ◽  
Quantile Regression Analysis ◽  
Changes Over Time ◽  
Over Time

Abstract. There is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming. Some studies concluded that average rainfall in Zimbabwe had declined by 10% or 100 mm during the last 100 years. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for (a) the early part of the rainy season, October-November-December (OND), and (b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and for the decline or increase during years with either high or low rainfall using quantile regression analysis. The Pettitt test has also been utilized to examine the possible existence of change or break-points in the rainfall time series. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of all the rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing of rainfall greater than the ninetieth percentile at another station. All the other stations had no changes over time in both the low and high rainfall at the annual interval. Climate change effects are therefore not yet statistically significant within time series of total seasonal and annual rainfall in Zimbabwe. The general perception about declining rainfall is likely due to the presence of multidecadal variability characterized by bunching of years with above (e.g. 1951–1958, 1973–1980) and below (e.g. 1959–1972, 1982–1994 ) average rainfall.

scholarly journals Recent Rainfall Trend and Abrupt Changes Over Cavally Basin (West Africa)

2021 ◽  
pp. 52-66
Author(s):  
Blé Anouma Fhorest Yao ◽  
Emile Gneneyougo Soro
Keyword(s):  
Rainy Season ◽  
Kendall Test ◽  
Study Data ◽  
Dry Season ◽  
Annual Rainfall ◽  
Homogeneity Test ◽  
Monthly Precipitation ◽  
Climate Trends ◽  
Significant Drop ◽  
Standard Normal Homogeneity Test

Aims: Analyze the recent variations in annual and monthly precipitation at 18 pluviometry stations in the Cavally river basin. Place and Duration of Study: Data of month and annual rainfall data of 37 years (1980-2016) collected from the National direction of Meteorology for Ivory Coast and Guinea and from https://app.climateengine.org/climateEngine for Liberia. Methodology: Statistical methods are used to highlight the evolution of cumulative annual rainfall and the distribution of the different seasons over the period 1980-2016. Hanning’s low pass, Mann-Kendall classic test, modified Mann-Kendall test, Mann-Kendall seasonal test and Standard Normal Homogeneity Test were applied to identify the existing trend direction and significance of change over time. Results: The periods 1980-1996 and 1997-2016 could be considered as wet and dry periods respectively (with a rainfall deficit of 18% after the break in 1996). In addition, we observe a decrease in rainy days of strong accumulation that lead to a significant drop in total annual rainfall. Finally, an abnormal increase in rainfall during the dry season months and a decrease in rainfall during the rainy season months. This indicates an intra-seasonal irregularity (shortening of the rainy season and prolongation of the dry season) of precipitation. Conclusion: The Hanning filter, M-K test and SNHT are non-parametric tests widely used in the study of climate trends. However, the additional consideration of serial autocorrelation (MM-K test) and seasonal trends (M-K-S test) allows to extend and refine the information on climate variability.

scholarly journals PENENTUAN MUSIM TANAM, JENIS VARIETAS, DAN TEKNIK BUDIDAYA TANAMAN PADI TERKAIT MITIGASI EMISI METANA (CH4) (Determination of Early Planting Season, Type Varieties, and Cultivation Techniques of Rice as Mitigation to Methane Emission)

2018 ◽  
Vol 24 (1) ◽  
pp. 1
Author(s):  
Lilik Slamet Supriatin
Keyword(s):  
Rainy Season ◽  
Growing Season ◽  
Dry Season ◽  
Wetland Mitigation ◽  
Annual Rainfall ◽  
Ch4 Emission ◽  
Ch4 Emissions ◽  
Cultivation Techniques ◽  
Planting Season

ABSTRAKEmisi metana (CH4) dari pertanian padi lahan sawah dapat dipengaruhi oleh faktor-faktor seperti cara pemberian air, pengolahan tanah, varietas padi, dan iklim. Pada penelitian ini dikaji tahap penentuan musim tanam, pemilihan varietas padi, dan tahap terakhir adalah teknik budidaya pertanian padi lahan sawah yang terkait mitigasi emisi CH4. Hasil kajian menunjukkan bahwa musim tanam padi pada musim kemarau menghasilkan emisi CH4 lebih kecil daripada di musim hujan dengan pengurangan emisi CH4 sebesar 18,13%. Indonesia yang memiliki tiga tipe pola curah hujan tahunan (monsunal, equatorial, lokal) mengakibatkan periode musim tanam rendah emisi CH4 berbeda antara tipe curah hujan yang satu dengan lainnya. Varietas padi Way apo buru adalah varietas yang menghasilkan emisi CH4 terendah tetapi tetap optimum dalam produksi gabah sehingga dapat dipilih menjadi prioritas pertama untuk ditanam. Teknik budidaya pertanian padi lahan sawah yang menghasilkan rendah emisi CH4 dapat dilakukan dengan membuat genangan air yang dangkal saja, dengan cara pemberian air berselang, dan kombinasi antara pemeliharaan padi, ganggang, tanaman paku air, ikan air tawar, dan bakteri metanotrof dalam satu petak lahan sawah (mina padi plus). Pemberian air dengan cara berselang menurunkan emisi CH4 pada musim kemarau sebesar 59,36% dan pada musim hujan sebesar 51,68% jika dibandingkan dengan pemberian air secara terus-menerus (kontinyu). Teknik budidaya mina padi plus mengurangi emisi CH4 sebesar 21,5 kg/ha/musim tanam dan bakteri metanotrof mengurangi emisi CH4 ke atmosfer sebesar 20-60 Tg. Sawah dapat dijadikan sebagai instalasi terbuka pengolahan udara berlimbah CH4. ABSTRACTMethane (CH4) emissions from rice cultivation can be influenced by several factors i.e. the provision of water, soil cultivation, varieties of rice, and the climate. This study will examine the determination of the growing season, the selection of rice varieties and cultivation techniques of rice agriculture-related wetland mitigation of the CH4 emission. The results showed that the rice planting season in the dry season produces CH4 emissions is smaller than in the rainy season with CH4 emission reduction of 18.13%. Indonesia, which has three types of annual rainfall patterns resulting in periods of low growing season CH4 emissions differ between types of rainfall each other. Way apo buru rice species are varieties that produce low emissions of CH4 but remains optimum in grain production. Cultivation techniques of rice farming rice fields that produce low emissions of CH4 can be done by creating a pool of shallow water only, by way of provision of water intermittent, and the combination of maintenance of rice, algae, plants salviniales, freshwater fish, and bacteria metanotrof in a wetland. The provision of water by intermittent lowering emissions of CH4 in the dry season by 59.36% and in the rainy season amounted to 51.68% when compared to the provision of water continuously (continuous). Mina padi plus cultivation techniques reduce CH4 emissions by 21.5 kg/ha/planting and metanotrof bacteria can reduce CH4 emissions to the atmosphere by 20-60 Tg. 

scholarly journals Investigating possible changes of extreme annual rainfall in Zimbabwe

2008 ◽  
Vol 5 (4) ◽  
pp. 1765-1785 ◽  
Author(s):  
D. Mazvimavi
Keyword(s):  
Global Warming ◽  
Regression Analysis ◽  
Water Resources ◽  
Quantile Regression ◽  
Rainy Season ◽  
Kendall Test ◽  
Annual Rainfall ◽  
Management Approach ◽  
Average Rainfall ◽  
Quantile Regression Analysis

Abstract. There is increasing concern about the perceived decline in rainfall which is sometimes attributed to global warming. Some studies have concluded that average rainfall in Zimbabwe has declined by 10% or 100 mm/yr during the last 100 yrs. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for a) the early party of the rainy season, October-November-December (OND), and b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and changes in extreme rainfall using quantile regression analysis. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of the major rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing rainfall for rainfall greater than the ninetieth percentile at another station. All the other stations revealed no changes over time in both the extreme low and high rainfall at the annual interval. Therefore, there is no evidence that the frequency and severity of droughts has changed during the 1892 to 2000 period. The general perception about declining rainfall is likely shaped by a comparison of the recent drought years (1980's–1990's) to recent wet periods (1970's). There have however been periods with similar dry years beyond the recallable memory, e.g. 1926–1936, 1940's. Crop failures and livestock losses attributed to declining rainfall are most likely due to poor agricultural practices such as production of crops in unsuitable climatic regions, degradation of rangelands partly due to increasing livestock populations. Rainfall in Zimbabwe has high inter-annual variability, and currently any change due to global warming is not yet statistically detectable. The annual renewal rate of water resources from rainfall has therefore not changed, and an adaptive water resources management approach is called to overcome problems arising from increasing water demand, and variability of available water resources.

scholarly journals Variation in Onset of Leaf Unfolding and Wood Formation in a Central African Tropical Tree Species

2021 ◽  
Vol 4 ◽  
Author(s):  
Bhely Angoboy Ilondea ◽  
Hans Beeckman ◽  
Joris Van Acker ◽  
Jan Van den Bulcke ◽  
Adeline Fayolle ◽  
...  
Keyword(s):  
Tree Species ◽  
Rainy Season ◽  
Cambial Activity ◽  
Wood Formation ◽  
Dry Season ◽  
Tropical Tree ◽  
Congo Basin ◽  
Leaf Phenology ◽  
Annual Rainfall ◽  
Tropical Tree Species

A diversity of phenological strategies has been reported for tropical tree species. Defoliation and seasonal dormancy of cambial activity inform us on how trees cope with water stress during the dry season, or maximize the use of resources during the rainy season. Here, we study the matching between leaf phenology (unfolding and shedding) and cambial activity for Prioria balsamifera, a key timber species in the Democratic Republic of Congo. In particular, we (i) evaluated the seasonality of cambial activity and synchrony of phenology among trees in response to climate and (ii) identified the seasonality of leaf phenology and its relation with cambial phenology. The study was conducted in the Luki Man and Biosphere Reserve, located in the Mayombe forest at the southern margin of the Congo Basin. Historic defoliation data were collected every ten days using weekly crown observations whereas recent observations involved time-lapse cameras. Cambial pinning was performed on ten trees during 20 months and radius dendrometers were installed on three trees during 13 months. Tree rings were measured on cores from 13 trees and growth synchrony was evaluated. We found that P. balsamifera defoliates annually with a peak observed at the end of the dry season and the beginning of the rainy season. The new leaves unfolded shortly after shedding of the old leaves. The peak defoliation dates varied across years from September 12 to November 14 and the fraction of number of trees that defoliated at a given time was found to be negatively correlated with annual rainfall and temperature; during the dry season, when precipitation and temperatures are the lowest. Wood formation (radial growth), was found to be highly seasonal, with cambial dormancy occurring during the dry season and growth starting at the beginning of the rainy season. Individual ring-width series did not cross date well. The within species variability of leaf phenology and cambial rhythms provides indication about resistance of the population against climatic changes.

scholarly journals A discrete wavelet spectrum approach for identifying non-monotonic trends in hydroclimate data

2018 ◽  
Vol 22 (1) ◽  
pp. 757-766 ◽  
Author(s):  
Yan-Fang Sang ◽  
Fubao Sun ◽  
Vijay P. Singh ◽  
Ping Xie ◽  
Jian Sun
Keyword(s):  
Time Series ◽  
Statistical Significance ◽  
Kendall Test ◽  
Wavelet Spectrum ◽  
Spatiotemporal Variability ◽  
Discrete Wavelet ◽  
Potential Evaporation ◽  
Monotonic Trend ◽  
Warming Hiatus ◽  
Synthetic Time Series

Abstract. The hydroclimatic process is changing non-monotonically and identifying its trends is a great challenge. Building on the discrete wavelet transform theory, we developed a discrete wavelet spectrum (DWS) approach for identifying non-monotonic trends in hydroclimate time series and evaluating their statistical significance. After validating the DWS approach using two typical synthetic time series, we examined annual temperature and potential evaporation over China from 1961–2013 and found that the DWS approach detected both the “warming” and the “warming hiatus” in temperature, and the reversed changes in potential evaporation. Further, the identified non-monotonic trends showed stable significance when the time series was longer than 30 years or so (i.e. the widely defined “climate” timescale). The significance of trends in potential evaporation measured at 150 stations in China, with an obvious non-monotonic trend, was underestimated and was not detected by the Mann–Kendall test. Comparatively, the DWS approach overcame the problem and detected those significant non-monotonic trends at 380 stations, which helped understand and interpret the spatiotemporal variability in the hydroclimatic process. Our results suggest that non-monotonic trends of hydroclimate time series and their significance should be carefully identified, and the DWS approach proposed has the potential for wide use in the hydrological and climate sciences.

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