HUMID REGIONS

12.3 HUMID REGIONS

(i) High intensity of rainfall (a.a.r. > 75 cm) with not much variability with respect to time and space. (ii) High precipitation, low temperature and minimum loss of water. Transpiration is the major water loss amounting upto 80%. (iii) Flow in streams is continuous and the ground water table is always above the bed level of the stream, i.e., the streams are mostly perennial. (iv) The ground water table is usually at very high elevation and the ground water con- tributes to streamflow. The change in ground water storage becomes significant. (v) Average annual yield can be satisfactorily determined from a comparatively short period of records. (vi) Best suited for irrigation and agriculture. Crops can be grown throughout the year due to availability of water supply throughout. (vii) A drought does not occur in ordinary years.

QUIZ XII

I Choose the correct statement/s in the following: 1 In an arid region (i) rainfall is mostly during summer

(ii) each fall of rain is considered as a separate unit (iii) drought-duration studies are essential (iv) major loss is by transpiration (v) ‘drip irrigation’ is preferred

(vi) ephemeral streams are common (vii) seasonal crops can be grown

(viii) all the above characteristics 2 In a semi-arid region (i) precipitation is only during winter or spring (ii) rainfall is only seasonal (iii) Intermittent streams are common (iv) ‘isopercentral maps’ are prepared for individual or isolated storms (v) seasonal crops like jowar, ragi, etc. can be grown (vi) flow-duration and drought-duration studies are essential (vii) Unit hydrograph method can be applied (viii) Gullying and stream-channel erosion is a characteristic feature (ix) all the above characteristics 3 In a humid region (i) uniformly high rainfall occurs

(ii) transpiration is the major water loss (iii) streams are mostly perennial

(iv) intensive irrigation is possible (v) drought normally does not occur

(vi) change in ground water storage is significant

HYDROLOGY (vii) high evaporation losses occur

(viii) all the above characteristics. [1—(v), (vi); 2—except (vii); 3—except (vii)] II Match the items in ‘A’ with items in ‘B’ (more than one item in ‘B’ may fit):

(i) Semi-arid region

(a) Arid region

(ii) Arid region

(b) Semi-arid region

(iii) Drip irrigation (c) Normally drought conditions (iv) Seasonal crops

(d) Transpiration–major water loss (v) Probability and duration studies

(e) GWT very high

(vi) Humid region

(f) High temperature (g) Low temperature

(h) Isopercentral map (i) Ephemeral streams (j) High evaporation losses

(k) a.a.r. = 40–75 cm (l) a.a.r. < 40 cm

III Say ‘true’ or ‘false’, if false, give the correct statement: (i) High evaporation losses are significant in arid regions while transpiration is the major water

loss in humid regions. (ii) In arid regions, the rainfall occurs mostly during summer and the rainfall (R) in cm is given by: R = T + 14, while in semi-arid regions, the rainfall is mostly during winter and spring and R lies between (T + 14) and 2(T + 14), where T is the annual average temperature in °C.

(iii) In arid regions, the infiltration capacity of the soil varies throughout the year. (iv) Ephermeral streams are quite common in semi-arid regions. (v) Salt-concentration problems occur in irrigated soils and hence water has to be applied to

crops by ‘drip’ or ‘sprinkler irrigation’ methods, in arid regions. (vi) Seasonal crops like jowar, ragi, etc., can not be grown in semi-arid regions. (vii) Probability and duration studies (drought duration and flow duration) are essential to deter- mine the available flow or drought period in a long-term climatological cycle (or swing) in

arid and semi-arid regions. (viii) Non-variability of hydrological factors with respect to time and space are characteristic fea-

tures of arid and semi-arid regions. (ix) In arid regions, the pattern of rainfall distribution (development of isohyetal map) can be

studied by ‘isopercentral map’. (x) Transposition of either the isohyetal pattern or depth-area values from one river basin to

another may give eroneous results in semi-arid mountainous regions. (xi) Unit hydrograph technique can be used for semi-arid regions. (xii) High precipitation (a.a.r > 75 cm) and low temperature are characteristic of humid regions

and crops can be grown throughout the year. (xiii) While drought is a usual state of affairs in an arid region, it does not occur in ordinary years in a humid region. (xiv) A drought occurs at least once in a year in a semi-arid region, except in abnormal years.

(false: iii, iv, vi, viii, ix, xi)

ARID, SEMI-ARID AND HUMID REGIONS

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