Study on the Uncertainty of Critical Rainfall for Flash Floods in Small Watersheds Based on the Random Rainfall Pattern

Flash floods cause great harm to people's lives and property safety. Rainfall is the key factor which induces flash floods, and critical rainfall (CR) is the most widely used indicator in flash flood early warning systems. Due to the randomness of rainfall, the CR has great uncertainty, which causes missed alarms when predicting flash floods. To improve the early warning accuracy for flash floods, a random rainfall pattern (RRP) generation method based on control parameters, including the comprehensive peak position coefficient (CPPC) and comprehensive peak ratio (CPR), is proposed and an early warning model with dynamic correction based on RRP identification is established. The rainfall-runoff process is simulated by the HEC-HMS hydrological model, and the CR threshold space corresponding to the RRP set is calculated based on the trial algorithm. Xinxian, a small watershed located in Henan Province, China, is taken as the case study. The results show that the method for generating the RRP is practical and simple, and it effectively reflects the CR uncertainty caused by the rainfall pattern uncertainty. The HEC-HMS model is proved to have good application performance in the Xinxian watershed. Through sensitivity analysis, the effect of the antecedent soil moisture condition, CPPC, and CPR are compared. The proposed early warning model is practical and effective, which increases the forecast lead time.

Effect of eastward moving cloud clusters over northwest India and neighbourhood on the Indian summer monsoon

A number of studies have been made relating to the prediction of date of onset and also the activity of southwest monsoon over India. In this study an attempt has been made to link the behaviour of rainfall in northern and peninsular India to the satellite cloud clusters over the region of Afghanistan, Iran and northwest India. The monsoon rainfall over India commences in June. Hence variation of monsoon rainfall pattern with the movement of cloud clusters from northwest in pre-monsoon and monsoon months have been studied to elucidate the pattern of changes. The variability of monsoon performance largely depends on the number and movement of cloud clusters over northwestern region during pre-monsoon and monsoon months.

Rainfall distribution and tea production in Bangladesh: Socio-economic impact analysis

The study aimed to assess the present pattern of tea production and the impacts of rainfall patterns on tea yield and made tea quality. The cost of production and profit-loss were examined to link with rainfall distribution. Likewise, the daily income of permanent workers, the job market of the contractual workers, and the workers' associated welfare were critically analyzed to understand the social impact. The Rangpur division showed an incremental dryness; in contrast, the Sylhet division showed a steady pattern with a high frequency of continuous heavy rainfall. The rainfall pattern of the Chottogram division was highly unpredictable and oscillated. Long spell drought and heavy showers followed by flash floods affect tea yield. According to respondents' perception, the rainfall pattern showed changing behaviours that are not favourable for tea production. The emergence of new pests and deterioration of soil characteristics were reported. Bangladesh enjoyed the most pleasant weather for tea production in 2019. The cost of production increased with the adverse weather, which increases the loss for the growers. Profit loss of growers is a determinant of the welfare of the workers impacting their livelihoods. The organic tea garden is not affected by climatic events. Consequently, the socio-economic conditions of the organic garden are safeguarded. Hence, the study recommends following organic farming to cope with climate change. Differently, it was reported that the intermediaries' hegemony in the market chain is more problematic than climate change. Policy initiatives are warranted to correct the market and to establish growers and consumers' rights.

The Effects of Rainfall Patterns on Runoff, Sediment, and Nutrients Under Various Artificial Rainfall Experiments

Assessing the effects of rainfall patterns on runoff, sediment, nutrients under variation of rainfall pattern are significant in the quantification of sediment transported by overland flow. Previous experimental and field works studied that sediment transport is influenced by hydraulic properties of flow, physical properties of soil and surface characteristics. This study aims at determining the effect of rainfall patterns on surface runoff, sediment loss and nutrient loss. Experiments were carried out using four rainfall patterns, namely Pattern A (uniform-type: 8-8-8 l/min), Pattern B (increasing-type: 7-8-9 l/min), Pattern C (increasing-decreasing-type: 7-9-8 l/min) and Pattern D (decreasing-type: 9-8-7 l/min) with the changes of intensity every 30 minutes that gives total rainfall duration of 90 minutes for each pattern. The simulation was performed in three repetitions. The average total runoff produced was 668.65, 701.40, 699.10, and 722.63 liters, for rainfall patterns A, B, C, and D, respectively. The trend of runoff generated was influenced by the rainfall patterns, Pattern D generated the highest amount of runoff meanwhile Pattern A generated the lowest. For total suspended sediment concentrations, the mean value among every three repetitions of rainfall pattern resulted as 14,518.88, 13,732.73, 8,011.71 and 19,918.50 mg/l for patterns A, B, C, and D, respectively Pattern D contributed to the highest amount of sediment accumulated whereby Pattern C generated the lowest sediment despite the trend showed a different approach than the other 3 patterns. In nutrient concentrations, the determined total losses for ammonia nitrogen were 3.986, 2.891, 3.504, and 4.601g; nitrate nitrogen were 3.934, 2.665, 4.008, and 3.259g; phosphorus were 1.346, 0.222, 0.207, and 0.679g, for patterns A, B, C, and D, respectively. In general, rainfall pattern does have a significant impact on the trend of nutrient losses, where the trend shows that higher concentrations at the start and eventually lowered through the end, but Pattern D as compared to other patterns resulted in a more severe nutrient loss. For the affected area of the soil movement process, the calculated means of the affected area are 79.60, 68.70, 72.43, and 64.97% for patterns A, B, C, and D respectively. The lowest mean of the affected area is contributed by Pattern D and the highest by Pattern A.

Incomplete Gamma distribution of rainfall for sustainable crop production strategies at Palampur, Himachal Pradesh

The knowledge of rainfall pattern (amount and probability) helps in planning of crops to be grown in a region. Therefore weekly, monthly, seasonal and annual rainfall data for 33 years (1974-2006) for the station Palampur have been collected and its analysis has been attempted. The annual and monthly rainfall data were analyzed for finding out drought normality and abnormality. The analysis indicated that the rainfall is mainly confined in annual rainfall 2343 mm with 25.7 per cent variability. The standard deviation of annual rainfall is 62.8 mm. Each standard week from 26th to 35th receive a rainfall of more than 100 mm, indicating the crop period. Seed sowing in paddy nursery in the Palampur region generally takes places immediately after initiation of monsoon during 23rd - 25th standard meteorological weeks and transplanting is carried out around 27th or 28th standard meteorological week. The tillering, 50 percent flowering and dough stage are observed during 32-33rd, 37-38th and 40-41st standard meteorological weeks respectively.