Pakistan Journal of Meteorology Vol. 7, Issue 13 53 Diagnostic Study of Heavy Downpour in the central part of Pakistan Muhammad Aleem-ul-Hassan 1 , Sajjad Haider 1 and Kalim Ullah 2 Abstract Diagnosis of heavy rainfall event of July 2005 that caused urban flooding in Multan City, located in Punjab province of Pakistan has been carried out in the study. By using the conventional weather charts of Pakistan Meteorological Department (PMD), National Centre for Environmental Prediction (NCEP) reanalysis data plots and analysis of temporal and spatial distribution of different weather parameters at the surface and in the upper air have been done. It is diagnosed that the heavy rainfall occurred under the influence of approaching monsoon depression, westerly wave prevailing over Kashmir and surrounding Himalayan region and its interaction with the upper air easterly wave. Besides this, the mesoscale low slightly northeast of the study area and an intensified ridge penetrating from northeast up to west of the study area, created the area of discontinuity that caused the interaction of northeastern and southwestern currents. The intensive heating in the last week of June and due to influence of westerly, a mesoscale low was formed in the leading trough of depression. The seasonal low was also realigned due to its interaction with westerly wave and the depression. Streamlines at lower level indicate that moisture transport from Arabian Sea was started two days prior to the event with maximum transport from 3rd July Night. On the basis of these synoptic features the amount of rainfall can be predicted well in time and therefore, it may help in minimizing the flood damages in the form of losses of human lives, soil erosion as well as managing the sewerage channels. Keywords: Conventional Weather Charts; Monsoon Depression; Mesoscale Low Introduction In the present world with increasing population, the demand of water is increasing day by day in various sectors like drinking water, industries, agriculture and many others. Pakistan is an agricultural country and its most of the economy, directly or indirectly depends upon the agricultural activities. Agriculture in Pakistan is directly linked with the amount of rainfall received during monsoon season. Widespread rainfall of moderate to heavy intensity was recorded for two consecutive days in Kashmir, Punjab and Khyber Pakhtun Khwa (KPK), while of light to moderate intensity was recorded at isolated places Sindh and Balochistan. In Pakistan the main contribution in the availability of water is the monsoon rainfall and also supplemented by the melting of glaciers. Heavy rainfall events affect the river flow and inundation as well as the sewerage systems of urban conurbation. The frequency of these heavy rainfall events is more in the upper parts of Pakistan as compared to the lower parts. Many studies have investigated the possible causes for the heavy rainfall events in different parts of Pakistan (e.g., Rasul et al., 2004, 2005; Majid and Akhtar, 2007; Sarfaraz, 2007; Jameel et al., 2007). Rasul et al., (2004) studied the weather systems causing extreme heavy rainfall over the twin cities of Pakistan (Rawalpindi & Islamabad) and proposed a physical model for sudden heavy rainfall. The monsoon depressions that originate over Bay of Bengal and Arabian Sea are the primary cause of rainfall over Pakistan during the summer season. The fluctuations in monsoon rainfall have a decided impact on the society and economy of monsoon dominated countries (Sajani et al., 2007). The heavy rainfall is often associated with organized mesoscale convective systems (Fang 1985; Iwasaki and Takeda 1993). Ninomiya and Akiyama (1992) widely considered that the mesoscale processes are more important in determining the actual behaviours of heavy rainfall systems. The heavy rainfall event over Multan City (300 12′ N Latitude and 710 26′E Longitude) has been selected for this study and an attempt has been made to understand the nature of rainfall events over that area. Furthermore, the main objective of this study is to improve the prediction of heavy rainfall which will be helpful in reducing the flood damages in future. Multan City is located in the southern part of the Punjab Province Pakistan where such kind of heavy rainfall events are 1 Pakistan Meteorological Department 2 COMSATS Institute of Information Technology.