Geographical factors such as topography and climate can have an effect on child mortality. For example, extreme climatic conditions where it is very cold or where there is very heavy rain can lead to higher mortality due to an increase in the incidence and severity of respiratory diseases (Meegama, 1980:8). Thus, it is important to look at the geographical condition in each region so that differentials in child mortality among regions can partly be explained by the geographical variations.
Thailand is situated in Southeast Asia between 5 and 21 degrees north of the equator, comprising about 514,000 square kilometers. The country is divided into four geographical regions with distinctive features. The following sections will briefly describe each region's geographical features.
2.2.1 The North
This region consists of a series of parallel and longitudinal folded mountain ranges in the northwest and west, respectively, forming the border between Thailand and Burma. To the east, the Luang Prabang Range forms the border with Laos. These mountains are densely forested.
Between the typical northern mountain ridges, there are relatively flat basins in which the main tributaries of the Chao Phraya River flow southward. The river valleys of the North show a specific form and are called intermontane plains. They all possess a substantial layer of alluvial soil, and have enough water to be suitable for growing rice, vegetables, tobacco and fruit trees (Donner, 1978:664-669).
The climate of the North is noticeably different from that of the neighboring Central region. The high mountain chains, rising steeply and running north-to-south, act as rain producers on one side and as dry weather promoters on the other, in the rain shadow, thus causing conditions which are alternatively humid and arid. In addition, in the absence of the
ocean and in the exclusively continental surroundings, tempera tures in the North are more variables than in Central Thailand. The temperatures comprise wide differences between mean maxima and mean minima each month. In addition, there are generally hot noons and rather cold nights (Donner, 1978:674-678).
2.2.2 The Northeast
The region is bordered by the Mekong River in the north and the east, by mountains in the south and the west. It comprises plains often called the Korat Plateau which can actually be divided into two clearly defined sub-regions, the southern Korat Basin and the northern Sakhon Nakhon Basin.
Two characteristics of the northeast hydrology are flood and drought. This is due to the modest gradient of the riverbeds, together with a layer of laterite under the topsoil, which causes water-logging and inundation as soon as the rainy season starts and begins to fill the river. In the rainy season many rivers seem to run in gorges. However, when the rain ceases, the rivers lose water rapidly. Thus, the lack of surface water in the northeast not only hampers agricultural activities but also leads to scarcity of drinking water for the people and animals (Donner, 1978:564-565).
Owing to its topography, the Northeast region has a special climatological condition. The Korat Plateau is locked off in the west and the south by mountain ranges. These
mountains form a c l e a r b ar r ie r a ga i n s t the southwest monsoon and consequently c r e a t e a rain shadow area i n the western part of the
r e gi on . Therefore, the temperature in the nor theas t i s more
extreme than in the Central p l a i n s , c o o l e r in winter and h o t t e r
in hot season.
2 . 2 . 3 The South
The South i s c h a r a c t e r i s t i z e d by mountain chains
running roughly north to south and mostly d i v i d i n g the pe ninsula
i n t o a western and an e a st e r n p a r t . The mountains form a rather
w e l l - c l o s e d uninterrupted b a r r i e r , thus loc ki ng o f f the west
co ast from the e a s t c o a s t a l p l a i n s .
The west c o a st i s mainly formed by mountain ranges
which come very c l o s e t o the sea and allow a l l u v i a l p l a i n s to
develop only in a few p l a c e s . I t p o s s e s s e s few beaches when
compared with the e a s t . In c o n t r a s t , the e a s t coast i s f l a t and
sandy, and though rocky h i l l o c k s o c c a s i o n a l l y appear c l o s e to the s h o r e - l i n e , the proper mountain range r i s e s w e l l inl and. The e a st
coast i s smooth and s t r a i g h t , i nt e rr up t ed only by r i v e r mouths
(Donner, 1978:413).
The p e c u l i a r shape of the r eg io n, s t r e t c h i n g over
f i v e p a r a l l e l s north-south between two oceans and s i t u a t e d in a
pronounced monsoon area, r e s u l t s in a cl imate of d i s t i n c t
c h a r a c t e r i s t i c s . The most important m e t e o r o l o g i c a l phenomenon
m a n y r a i n - c a t c h i n g m o u n t a i n ranges, the b u l k of the rain falls on the west coast duri n g the sou th wes t m o n s o o n and on the east coast d u r i n g the nor t h e a s t monsoon. Th ere fo re, the h e a v i e s t rai nfa ll r e c o r d e d in T h a i l a n d oc cur s on the p e n i n s u l a r west coast. The re gio n has a cl as si cal m a r i t i m e c l im ate wh i c h is in con tra st to othe r region s of the country. It is c o m p a r a t i v e l y w a rmer in w i n t e r in the west and c o m p a r a t i v e l y w a rm er in su mme r in the east.
2.2.4 The Central Region
Due to its g e o g r a p h i c a l location, this re gi o n can be d i v i d e d into two sub- reg ion s. The first s u b - r e g i o n or the so cal l e d "cen tra l plains " com p r i s e s the cen tra l and w e s t e r n parts of the country, c o v e r i n g m a i n l y the v a l l e y of the Ch ao Pr ay a river and its tributarie s. The s e c o n d s u b - r e g i o n is the s o u t h e a s t e r n p o r t i o n of the region.
A. The Central Plain
This is a good area for rice cul ti va ti on, c o n s i s t i n g m a i n l y of flat alluvi al plains close to sea level and subje ct to floods d u ring the annual m o n s o o n season. In the w e s t e r n part of the plain, there are mou n t a i n s wh ic h are d e n s e l y fo re s t e d and b a r e l y a c c e s s i b l e except on foot or by boat al on g c er ta in rivers. Th e s e m o u n t a i n s define the bor der be t w e e n T h a i l a n d and Burma. T h e y sh iel d the region from the so ut hw est m o n s o o n and cyc lones. T owa rds the north, the ce ntr al plain is b o r d e r e d by a n ot her
strip of marginal uplands and terraces, foothills of the northern folded mountains.
Despite the heterogeneous topography, that is the extensive low plain not rising much above sea level, the mass of water of the Gulf of Thailand in the south, and the high mountains in the west and the north, the region's weather is rather homogeneous. The temperature generally reaches its maximum in April throughout the region, and then continuously decreases until it reaches a minimum in December (Donner, 1978:241).
B. The Southeastern Part
The sub-region consists for the most part of flat lowlands below 100 meters. It is bounded to the north by mountain ranges which are still densely forested and scarcely populated. The northern part of this sub-region is characterized by its contact with the Central plains. On the other hand, the southern part of the sub-region consists of an extensive lowland, interrupted by isolated mountains and ranges in the west and mountain massifs in the east.
The sub-region shows a number of interesting climatological characteristics. The northern part is to some extent sheltered by the northern and southern mountain massifs, whereas the southern part is fully exposed to all the meteorological influence coming from the south and the west.
Therefore, the northern part of the sub-region receives less rainfall, whereas the extreme southeast part receives the highest rainfall. With regard to temperature, the mean temperatures are fairly uniform and the fluctuations from day to day or month to month are smaller than in many parts of the country.