Rainfall Warning Research Articles

The Reasoning and Application Model for Topological Relations between a Concave Region and a Simple Broad Boundary Region

According to the nature of 16 - the intersection model and the constraints of the broad boundary region, get 67 topological relations that can be realized between a concave region and a simple broad boundary region. We realize the reasoning of topological relations between a concave region and a simple broad boundary region, and establish topology model of typhoon rainfall warning, and provide reference for expand of the related topology model applications.

A quantitative analysis of KALPANA-1 derived water vapor winds and its impact on NWP model

The coverage of satellite derived winds over the Indian region including Indian Ocean has improved by the operation of India’s first dedicated satellite for meteorology, KALPANA-1 since 12 September 2002. Atmospheric motion vectors (AMVs) are being derived at the India Meteorological Department (IMD), New Delhi on a routine operational basis. The AMV is recognized as an important source of information for numerical weather prediction (NWP) and is particularly suited for tracking the low and middle level clouds mainly because of the good contrast in albedo between target and background, whereas the upper level moisture pattern can be better tracked by water vapor winds (WVW) using water vapor (WV) channel (5.7–7.1 μm). The WVWs proved to be a very useful wind product for predicting the future track position of cyclones, well marked low pressure areas or heavy rainfall warnings in advance and so, often these types of weather systems are steered by the upper level winds. In the present study, the quantitative as well as qualitative analyses of KALPANA-1 WVW have been carried out. The primary change introduced is making use of first guess (FG) forecast fields obtained from National Center for Environmental Prediction (NCEP) and Global Forecast System (GFS), at a resolution of 1° × 1° with T-382/L64 instead of forecasts of operational limited area model (LAM) of IMD. The overall results showed a consistent improvement after using improved FG wind fields from NCEP instead of LAM with a significantly increasing number of good qualities of KALPANA-1 derived WVWs. The quantitative error analysis has also been carried out for the validation of WVWs using collocated radiosonde observations for the period from May 2008 to December 2009 and the available mid-upper level winds derived from METEOSAT-7 data for the period from October to December 2008. The analysis shows that after modification, the RMSE and bias of KALPANA-1 WVWs have reduced considerably. Further, to assess the impact of these winds, a high resolution mesoscale model WRF 3DVAR system is used in the present study for the analysis of tropical cyclone ‘Sidr’. The results show that the wind assimilation experiments (analysis at 200 hPa) using upper level KALPANA-1 WVW have great potential for improving the NWP analysis. The impact of additional wind data in the model is found to be positive and beneficial.

TIGGE 모델을 이용한 한반도 여름철 집중호우 예측 활용에 관한 연구

The predictability of heavy precipitation over the Korean Peninsula is studied using THORPEX Interactive Grand Global Ensemble (TIGGE) data. The performance of the six ensemble models is compared through the inconsistency (or jumpiness) and Root Mean Square Error (RMSE) for MSLP, T850 and H500. Grand Ensemble (GE) of the three best ensemble models (ECMWF, UKMO and CMA) with equal weight and without bias correction is consisted. The jumpiness calculated in this study indicates that the GE is more consistent than each single ensemble model. Brier Score (BS) of precipitation also shows that the GE outperforms. The GE is used for a case study of a heavy rainfall event in Korean Peninsula on 9 July 2009. The probability forecast of precipitation using 90 members of the GE and the percentage of 90 members exceeding 90 percentile in climatological Probability Density Function (PDF) of observed precipitation are calculated. As the GE is excellent in possibility of potential detection of heavy rainfall, GE is more skillful than the single ensemble model and can lead to a heavy rainfall warning in medium-range. If the performance of each single ensemble model is also improved, GE can provide better performance.

Rapid Flood Evaluation Systems in Taiwan Metropolitan Areas

Hydrological issues in metropolises in Taiwan have become increasingly important because the storm water sewer systems of metropolises are frequently unable to meet the requirements of the existing and future metropolitan development. Typhoons or torrential rains that cause rainfall intensities that exceed the designed capacity of storm water sewers can result in serious flooding. The losses caused by flooding can be reduced if the areas at risk of flooding can be predicted and warnings can be issued to prompt disaster prevention and allow response units and residents to prepare before disasters occur. The primary purpose of this study is to integrate the quantitative precipitation forecasting technologies [1, 2] developed by the Taiwan Typhoon and Flood Research Institute to establish a rapid, stable, real-time, and automatic metropolitan area flood estimation system for predictive flooding analysis. The objects of this study are metropolitan areas in Taiwan with storm water sewer systems. The standard capacities of storm water sewer systems throughout Taiwan and the geographic information system (GIS) shape files are collected and compiled. Additionally, the potential flooding areas are divided into four levels (high, medium, low, and no flooding) and are compared with the rainfall warning values of the Water Resources Agency. The study combines the results of quantitative precipitation forecasts, establishes an information database (MySQL), processes Google Earth KML files, and designs a WEB GIS display interface to construct a system for estimating the flooding possibility (probability) in metropolitan areas during typhoons or torrential rains. This study subsequently employs the event of Typhoon Kalmaegi for flooding estimation and display; the estimation results are consistent with the flooding survey data, indicating that the estimations made by the flooding estimation system are correct.

A composite approach of radar echo extrapolation based on TREC vectors in combination with model-predicted winds

Extending the lead time of precipitation nowcasts is vital to improvements in heavy rainfall warning, flood mitigation, and water resource management. Because the TREC vector (tracking radar echo by correlation) represents only the instantaneous trend of precipitation echo motion, the approach using derived echo motion vectors to extrapolate radar reflectivity as a rainfall forecast is not satisfactory if the lead time is beyond 30 minutes. For longer lead times, the effect of ambient winds on echo movement should be considered. In this paper, an extrapolation algorithm that extends forecast lead times up to 3 hours was developed to blend TREC vectors with model-predicted winds. The TREC vectors were derived from radar reflectivity patterns in 3 km height CAPPI (constant altitude plan position indicator) mosaics through a cross-correlation technique. The background steering winds were provided by predictions of the rapid update assimilation model CHAF (cycle of hourly assimilation and forecast). A similarity index was designed to determine the vertical level at which model winds were applied in the extrapolation process, which occurs via a comparison between model winds and radar vectors. Based on a summer rainfall case study, it is found that the new algorithm provides a better forecast.

Suspended sediment transport regime in a debris-flow gully on Vancouver Island, British Columbia

In debris-flow-prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris-flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s−1, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ‘supply limited’; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain-on-snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd.

Development and evaluation of the forecast step of the FRONTIERS short-term precipitation forecasting system

Abstract The development of the forecast step of the FRONTIERS precipitation nowcasting system is described. In particular, an option to advect the precipitation field with forecast winds has been introduced. Routine evaluations indicate a consistent improvement in forecast accuracy, relative to persistence, following the upgrade. Forecast accumulations are evaluated by comparison with raingauge data in two regions of the UK. In the North West, they are compared with heavy rainfall warnings issued operationally. The operational forecasts were significant overestimates (average bias +250%) but were issued more reliably than were the FRONTIERS forecasts, which were much closer to ground truth for the same cases (average bias −29%). Comparison with a dense gauge network in the South East shows that the accuracy of the forecasts increases with increasing accumulation period and catchment size.

Torrential Rains in Central Karakoram, 9-10 September 1992. Geomorphological Impacts and Implications for Climatic Change

The exceptional rains in the northwestern Himalaya, and subsequent Indus Basin floods of September 1992, were widely reported. Some attributed the damages simply to unprecedented rainfall. Preliminary reports do indicate higher precipitation in the Jhelum catchment than during the disastrous floods of October 1955 and August 1973, but less rain in the headwaters of the Ravi, Chenab, and Sutlej (Johnson, 1979: 87-90; Hewitt, 1983). Others attribute the scale of the disaster mainly to human factors: to deforestation in the Himalaya (Adil, 1992; Ilyas, 1992) and to an extraordinary and massive release of water from Mangla Dam (Abbas, 1992). The lack of preparedness was surprising, given the long history of flood forecasting and control projects here. Severe rainfall warnings were issued in India for Himachal Pradesh, and Jammu and Kashmir (Times of India, 8 and 9 September 1992), but apparently not in Pakistan. The conditions in the transhimalayan valleys of the Karakoram received much less notice, because of timing and the greater human losses to the south. Torrential rains in the Front Ranges occurred 12-24 hours earlier. The sharp rise of the Jhelum River began between 0600 and 0800 hours on 9 September at the Mangla Dam. The sudden release from the reservoir was implemented that evening, when torrential rains were just beginning in the transhimalayan valleys (Abbas, 1992: 29). Continuous, exceptionally heavy rain in the Braldu valley, Central Karakoram, was observed from about 1800 hrs on the 9th until 0530 on the 10th. Almost all geomorphic activity and damages described below occurred during that night, when the enormous sounds of mass movements went on unabated. Moreover, the rainfall in this region was exceptional in amount, intensity, geographical extent, timing, and erosional impacts. Torrential rain was reported throughout Gilgit, Hunza-Nagyr, and Chilas districts, as well as Baltistan. EVENTS, 9-10 SEPTEMBER 1992 Measured precipitation in the Karakoram far exceeded existing records, as indicated by Table 1 which shows the rainfall amounts measured at Chilas and Gilgit. The storm period precipitation to the south was much greater. At Abbotabad, it was 390 mm; at Murree, 326; Srinagar, 104; andJammu, 146. However, for the southern flank of the Himalaya this was relatively much less extreme.

Rainfall over Bombay associated with cyclonic storms striking Saurashtra coast

Normally heavy rain is expected over the field of depressions and cyclonic storms. On this basis, it is comparatively easy to issue heavy rainfall warnings sufficiently in advance, whenever disturbances in the Arabian Sea and Bay of Bengal show a tendency to move towards the coast. It was observed by Mukherjee, et el. (1966) that cyclonic disturbances striking south Tamil Nadu coast during October, bring adequate supply of moisture to cause heavy rainfall in far away coastal Andhra Pradesh. Applying the same analogy, this paper tests the theory whether the cyclonic storms striking Saurashtra coast can cause heavy rainfall in Bombay. It is found that during the last 85 years, seven cyclonic storms struck Saurashtra crest during the pre-monsoon months April and May and the post-monsoon months October and November. All of them caused good rainfall over Bombay, This has been tested for Bombay due to its importance as a metropolis. The results were always found to be positive. The phenomenon has been explained taking into consideration the characteristics of air flow connected with these systems.

Isohyetal Patterns over South India in relation to the locations of various Storms/depressions of the Bay striking east peninsular coast during Post monsoon season

In this paper, a study has been made of the isohyetal patterns over South India during the post-monsoon season in relation to the position and movement of Bay storms/depressions. The above disturbances have been classified into three categories, viz. , A, p and C according to their crossing the coast south of Cuddalore, between Cuddalore and Ongole, and between between Ongole and Cahngapatnam respectively. The positions of the disturbances in the various 2-degree square in the Bay and the corresponding mean isohyetal patterns over South India during the subsequent 24 hours are shown diagrammatically for all the three categories. These diagrams may be of use to forecasters in issuing heavy rainfall warnings for the next 24 hours in association with the Bay disturbances during monsoon season.