Pakistan is a large country, about one and a half times the size of France. It is situated in the northwestern part of the great Indian subcontinent.
Its western border with Iran and northwestern border with Afghanistan are mountainous, and its short northern border with China and its northeastern border with India in the Pamir and Karakoram ranges include some of the higher Himalayan peaks. On the south and east it has a long border with India; this is a region of low-lying plains, part of the great Indus Valley.
Most of the country has a climate dominated by the influence of the great seasonal wind reversal called the Asiatic monsoon. (For a fuller description of this see India). The year may be divided into three principal seasons. From mid-October until late February is the cool season, when the weather is generally pleasant, sunny, and quite warm by day but with chilly nights and occasional frost.
The northern and western parts of the country receive some rain at this time, brought by depressions moving in from the west. Conditions in the higher mountains at this time are distinctly cold. During this period midday temperatures in the south and centre of the country rise to very high levels.
The heat is distinctly unpleasant in spite of the low humidity. Some occasional rain, usually of a showery, thundery type, may occur at this time. Such brief storms are often preceded or accompanied by dust storms. The rainy season over most of the country is from late June until early October. This is the season of the southwest monsoon and although temperatures are a little lower the higher humidity can cause discomfort.
Not all parts of Pakistan are equally wet during the rainy season. The desert region of the south and southeast receives little rain at this time and is sunny and hot; see the table for Jacobabad, which has the reputation of being one of the hottest places in the world from April until September.
Karachi, on the coast of the Arabian Sea, also gets little rain and, although cooler than inland, has a very unpleasant climate at this time because of the higher humidity. The mountainous regions of the north and west of the country receive much less rain during the period of the southwest monsoon and may be wetter during the cooler winter season.
See the table for Peshawar, which has a sequence of weather throughout the year more like that found in Iran, to the west.
It is in the eastern and central plains of the country that the full effect of the monsoon rains is felt. Here the climate throughout the year is more akin to that found in the northern plains of India (see the table for Islamabad).
Sunshine amounts are high around the year in most of Pakistan, ranging from six to seven hours a day in the cool season to ten to twelve during the hot season. There is an increase in cloudiness over most of the country during the wet season, even though rainfall amounts may be small in some areas.
For example, in July and August daily sunshine hours average only four or five at Karachi, even though the rainfall is much less than in the north of the country.
Snowfall is heavy on the higher mountains in the north but reliable measurements of its actual depth are not available. The melting snow from these mountains, together with the heavy summer rainfall from the monsoon, feeds the five great rivers of the Punjab plains which unite to form the Indus.
Were it not for the irrigation flow from these rivers, much of the Punjab and Sind lowlands would be a more extensive desert than they are.
In the hottest parts of Pakistan there is a danger of heat exhaustion or even heatstroke during the hot season and visitors should allow themselves a few days to become acclimatized before engaging in strenuous exercise. The heat is often so great that, without air conditioning, indoor temperatures at night are very uncomfortable.
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