SUMMER SEASONS:

When summer comes, the rays of the sun fall vertically in the plain areas of our country, the air when heated expands becomes high and develops a low pressure areas in south western part of Pakistan. Thus in the month of July lowest (994.7 Millibars) pressure is found around Multan and (29.40”) (29”45 inches) or (996.0 Millibars) near Lahore & (30.00” inches) or (997.7 Millibars) southward Karachi. As low pressure prevails over the land and comparatively high pressures over the neighboring cooler oceans, so to fill up the gap of low pressure found on the land areas, the cooler heavier air from high pressure areas of the ocean, known as summer monsoon, brings rainfall in our country.

WINTER SEASON:

During winter months the temperature over the land gradually increases and a high pressure gets very low and the pressure over the area is created in the north west of Pakistan. In January, the pressure at Peshawar, 30”. 15 inches or (1024.6 Millibars) and at Lahore 30”. 15 inches or (1017.4 Millibars) and near Karachi it is 30”. 4 inches or 1017.3 Millibars). Thus during winter months the winds from north to south began to prevail; these are known as winter monsoon. As these winds blows from land towards the sea, so they are mostly dry.

RAINFALL:-

The northern mountains and south western region & also the western part of Indus plain get food amount of rain from western disturbances or cyclone winds coming from the Caspian Sea, areas during winter months, e.g. the rainfall of Peshawar for the year is 33.1 cm., out of which 23.1 cm. from January to March and 11cm up to July.
Similarly in northern Balochistan winter rains are more important than summer rains. The annual rainfall of Queta is 24.4 cm. Out of which 17.5 cm. is received during December to July. The rain fall received in our country is not distributed evenly throughout the country. Most of the rainfall is received during the months of July to September, but a small amount of rainfall comes during winter months, from December to March, as rainfall is generally concentrated in a few monsoon months. The winter rain falls in heavy showers and much of the runs off the surface without sinking in the ground. The rain in our country varies from year to year.

CLIMATIC REGIONS OF PAKISTAN

INTRODUCTION

In Pakistan humidity is mostly low and they air is dry for the greater part of the year. Only in coastal areas lied Karachi, there is enough amount of humidity throughout the year. Thus keeping in view the various climatic factors Pakistan can be divided into the following climatic regions:

1. SUB-TROPICAL CONTINENTAL HIGLAND TYPE:

     The region includes the mountains in the north and west of the Indus plain. In this region winters are cold and lengthy and often the temperature goes below the freezing point; and the higher peaks remain snow-covered throughout the year. But here summer remains short, cool and temperate. The northeastern mountainous areas (Murree and Hazara division) receive enough rainfall throughout the year, but the maximum rainfalls during the summer months. Thus the northwestern areas have less amount of rainfall as compared to north eastern mountains, e.g. from south of Kohat and Waziristan rainfall decreases, so Queta division in Balochistan has a dry climate and there the mean annual rainfall is not more than 50 to 100 millimeters, it mostly comes during winter and spring.
     In these areas winters are cold & summers are hot. The northwestern mountainous areas receive lower rainfall, that is why these are less fertile and have barren rocks without any natural vegetation. Due to some rain in winter and spring some grass and shrubs appears which promotes the rearing of sheep and goat.

2. SUB-TROPICAL CONTINENTAL PLATEAU TYPE:

     This region includes the northwestern part of Balochistan province. Here winters are cold, and in summer temperature goes higher altitude, but due to poor rainfall, these have turned in to arid desert. In these areas there is a scarcity of rain water and it is less than 10” inches or 25 cm annually, but in some of the places of these areas have the lowest rainfall e.g. Nokundi has only 1.95 inches or 5 cm of rainfall annually, and rain often comes during the months of January & February.

3. SUB-TROPICAL CONTINENTAL LOW LANDS TYPE:

     This region includes the interior areas of Punjab and Sindh provinces. It has generally arid and extreme climate. Here summer remains long and hot, but winters are cool and short. It has the hottest places of the country, such as Jacobabad or Sibi.
     The rainy season begins in the middle of the summer months. The places, which are situated near piedmont areas, have enough rainfall, i.e. Sialkot has about 30 inches or 88.3 cm of annual rainfall. But the western part of this plain is drier than the eastern due to very poor rainfall, e.g. Thal and Cholistan desert in Punjab and Nara and Tharparkar desert in Sindh.

4. SUB-TROPICAL COASTAL AREA TYPE:-

     This region includes the coastal strip around Karachi and Makran coast in Balochistan. Here due to the influence of the sea, the temperature remains moderate; the rainfall is about 7 inches of 18 cm annually, but due to proximity of the sea, a large amount of humidity remains in the atmosphere. The influence of sea breeze during daytime is felt throughout the summer.