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Traditional design method for urban drainage systems is based on design storms and its major drawback is that frequencies of peak flows in the system an considered equal to frequencies of design storms. An alternative is to use historical storms with rainfall-runoff models to produce a series of possible flows in the system and their frequencies. The latter approach involves more computations and can be laborious for larger catchments. This paper considers ways to reduce the set of historical storms to be involved in design procedure and yet to lead to realistic flow frequencies. Frequencies obtained by rainfall-runoff simulation at an experimental catchment are compared with frequencies of observed peak flows in the system. (c) 1998 Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

Statistical models have been used to provide operational seasonal forecasts of rainfall over southern Africa since 1992. The Climatology Research Group has been using a quadratic discriminant analysis modelsince November 1994. The model relates rainfall over different areasof South Africa to principal components of sea-surface temperatures in the Indian, South Atlantic and Pacific Oceans. Details of the model are described in this paper. High forecast-skill levels can be achieved for much of the country throughout the year. The mostly successful performance of the model over a 15-year independent testing periodindicates that the model can be used successfully in an operational environment. [ABSTRACT FROM AUTHOR]

The pre-monsoon thermal field over the Indian landmass has an important bearing on the land-sea heating contrast in the region, consequently influencing the establishment, advance and overall performance ofthe Indian summer monsoon rainfall. This paper examines the relationship between the pre-monsoon thermal field over India and the following summer monsoon rainfall, in order to identify possible predictors for long-range forecasting of Indian summer monsoon rainfall. Based on the spatial patterns of correlations of monsoon rainfall with maximum and minimum temperatures at 121 stations well distributed over India, during the recent period 1951--80, two predictors showing a significant contribution to the variance in monsoon rainfall have been identified. They are (i) March minimum temperature in east peninsula India and (ii) May minimum temperature in west central India. These two predictors have performed very well in terms of their significant contribution to the multiple regression models during 1951--1987, vis-a-vis several other known predictors. They have also shown a consistently significant relationship with the monsoon rainfall during the recent period, from the mid-1940s till the end of the data period. A stepwise regression model for long-range forecasting of all-India summer monsoon rainfall, involving three regional predictors, has been developed, and has shown a multiple correlation of 0.89. ) 1997 by the Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

Much of New Zealand's precipitation is modulated by windflow, over its orography. Rain-gauge networks are normally sparse, and because measurement programmes are relatively expensive, there are considerablebenefits in modelling and mapping spatial patterns of precipitation in order to provide information at sites where no data exists. In this paper a simple, numerically robust diagnostic model (VDEL) for estimating orographic precipitation is used to estimate annual precipitation normals for a mountainous region of the southern North Island, New Zealand . The VDEL model, developed initially to analyse storm precipitation patterns, is based on the estimation of orographically forced vertical motion as V s -VZ s where VZ s is the height of the terrain and V s the low-level horizontal windflow upstream of the mountain range. Precipitation patterns were diagnosed by VDEL for four main windflow directions andcalibrated against annual precipitation normals by means of a multivariate regression mapping function. Areal average precipitation, mated from catchment runoffs, was reproduced with errors in the 5 to 10 per cent range. [ABSTRACT FROM AUTHOR]

In his comment on my paper, Whetton argues that precipitation estimates for the Southern Ocean (high latitudes of the Southern Hemisphere) in the Legates and Willmott climatology are implausible owing to its large seasonality. Justification for this assertion includes comparisons with island observations and methodological limitations he feels exist in the Legates and Willmott climatology. In this reply, the methodology used by Legates and Willmott is examined carefully and Whetton's concerns about it are shown to be his misinterpretation of theintent of the air temperature correction. Our (Whetton's and my) arguments serve to illustrate that observational evidence of precipitation over the ocean expanse of the Southern Hemisphere is a major limiting factor of all observation-based climatologies. [ABSTRACT FROM AUTHOR]

This paper updates precipitation series for England and Wales, Scotland and Northern Ireland for 1990 to 1995. A new precipitation seriesfor the whole of Ireland for 1840 to 1995 is developed. Recent changes in seasonal precipitation totals in all three regions are discussed. In all regions, recent precipitation in winter (DJF) has increasedand summer (JJA) precipitation has decreased. This trend is most evident in Scotland, where the November to April total for 1986 to 1995 is 30 per cent more than corresponding values in 1951 to 1980. For England and Wales the 1995 summer was the driest on record, with 7 mm less rainfall than in 1976, the previous driest summer. Over Scotland and Ireland the 1995 summer was also dry but not as exceptional. [ABSTRACT FROM AUTHOR]

The paper addresses issues relating to the design and calibration ofprecipitation models for down-scaling General Circulation Model (GCM) output. First, the significance of non-stationary daily circulation-pattern-precipitation relationships will be described for two UK sites, each with records beginning in 1881. Second, the cause(s) of the observed non-stationarity will be investigated using lengthy air flow, synoptic, temperature, and standardized teleconnection indices. Third, the prospects for incorporating these factors within down-scalingmethods will be discussed with reference to several alternative techniques. Finally, a multivariate approach incorporating teleconnectionand airflow indices within precipitation models is advocated. [ABSTRACT FROM AUTHOR]