Heat from the sun vis-à-vis evaporation and rainfall: Cause and effect

Sun is the source of all energies. Heat  from the sun is the driving force in the earth’s hydrological cycle. It is due to the attraction of the sun that earth and the other planets move in their respective orbits. The amount of heat received from the sun depends upon

1) the length of the day  and 2) the sun’s meridian altitude.

These two directly affect evaporation from earth’s surface. The earth is most heated when the daytime is longest and the reverse is the case when the day-time is shortest.  Again when the sun’s rays strike the surface of the earth nearly perpendicularly a pencil of rays covers a smaller portion of the earth’s surface than it would cover when the rays come obliquely ; moreover in the latter case the rays have to pass through a greater extent of the atmosphere and, therefore, lose more heat.  In spring and summer the sun is above the horizon for a longer period and the sun’s meridian altitude is greater than that in autumn and winter.  So, the spring and the summer are warmer than he autumn and the winter.

In the southern hemisphere the same season occurs in the opposite time of the year. Thus, for example, December, the winter month in the northern hemisphere, is the summer month in the southern hemisphere.

These seasonal changes also vary from year to year. Thus, there would be annual variation in hydrological parameters like evaporation, rainfall, etc.

So, in search of a pattern exclusively in annual rainfall series is possible. Taking into account of other meteorological variables like temperature, as we often propose, may give more perfection in predicted result from the analyzed trend in annual rainfall pattern, if any.

So,while working on the periodicity in New Zealand-rainfall Tomlinson (1980) have justifiably commented that we are all constantly making judgments and decisions on the basis of incomplete information, but this is preferable to decisions based on no information at all.  Statistical predictions of future rainfall should be seen in this light.  Predictions of future conditions can be made for at least three reasons: to test hypothesis, for planning purposes  and to attempt to avert catastrophes.  In the case of future rainfalls, concern should be with the first and possibly the second of these objectives

Studies on Studies on Rainfall Periodicity and Groundwater Recharge

The Enhancement of Rhythm - Rabindranath Tagore
– Rabindranath Tagore





1.1  Agriculture is mostly dependent on rainfall. If rainfall is adequate,   good crops are expected. For proper crop planning, advance information regarding rainfall   is very helpful.   Accordingly,  it  is necessary  to  undertake  investigations  for  evolving  a proper methodology  for  forecasting annual  rainfall.

1.2  The   analysis   of   the   periodicity  of  rainfall  has  evolved through  human  beings’   continuous  strides  over  predicting  any change in   climate   and   has   passed  through  speculation  based on   past experiences  in  the   mythological   period     (e.g.   .  mythical Khana  in India);   postulations  and  hypotheses  in  the  ancient historical period; and  indexing, probability,   correlation  and  regression  studies  and some  trials  on  physically  based  models  in  the  recent  years.  We  are all   constantly  making   judgments   and  decisions  on  the  basis  of incomplete  information;  but this  is preferable to   decisions based on no  information  at  all.   Statistical prediction of future rainfall should be   seen  in  this  light.  Prediction of  future  condition can be made  for  at least  three  reasons:   to  test  hypotheses;  for planning purposes;   and   to   attempt   to avert   catastrophes.   In   the   case   of future  rainfall,  concern  should  be  with the  first and  possibly  the  second  of  these  objectives.

1.3  The  objective  of  this   investigation  is  to  examine  the  nature  of  changes   of   rainfall   from  year  to  year.   Usually  these  changes  are  periodic,   i.e.   it  does  not  usually  follow  any  regular  increasing  or  decreasing         trend  but  with   some   type   of   cyclic   changes  having  excesses  and deficits.

1.4  Rainfall   penetration   through  surface  of  the  earth  is  one  of  the  major  factors  for  assessing hydrological  balance  for a particular  area.   This   factor   also  helps  to  assess  the  groundwater  resource through  the  estimation of  recharge.  There are many empirical  formulae for  estimation  of  this  factor,  but  these  are  not   universal  in their  application  regarding   their  methodologies.   So,   the   evaluation  of  a  new  method   is  needed   considering  basic flow  characteristics  of  soil water such as  hydraulic  conductivity.

In  the  present  studies  an  attempt  is  made   for  estimating rainfall   recharge  to   groundwater  from  daily   soil   moisture   flow through   solution  of  Darcy’s  equation  and  comparing  this  method with the  potential  recharge  from continuous  supply of water;  recharge  from water balance  and recharge  from groundwater table depth.

1.5  Irrigation water is  one  of  the most vital   inputs   in agricultural   production.  So,  the  scientific  utilization  of  this resource  will  hold  the  key  to  intensive  sustainable  agriculture  in the  ensuing  years  to  come.  For this purpose, the prediction of  annual rainfall   and   formulation  of  new   methods   for  more  accurate estimation  of   rainfall   recharge   to groundwater are   two   most  important   factors   for  planning   of   water   resources   in   any   region leaving  aside  surface  water  resource.

1.6  With  this background   in  view   the  present   investigation  has  been    taken up to  meet  the  following  objectives:

1.     Prediction  of  annual  rainfall  in Eastern  India –

i)  modeling  of  annual  rainfall  series,

ii)   identification  of   excess  and  deficit  runs  of  annual  rainfalls,

iii)  effect of  latitude  and  longitude on   periodicity in  annual   rainfall.

2.    Estimation of  groundwater  recharge  from rainfall –

i)  estimation of  potential   recharge,

ii)  estimation of  recharge  from water balance,

iii)  estimation   of recharge   from groundwater  table  depth,

iv)  estimation of  recharge   from soil moisture  flow,

v)  comparative   studies  on   four  different  methods  for  estimation  of  groundwater  recharge,

vi)  estimation  of   groundwater   recharge  from  annual rainfalls,

vii)  estimation   of   predicted annual  groundwater recharge from predicted annual  rainfall,

viii)  examination   of   acceptability   of   predicted groundwater   recharge from the   estimated             groundwater  recharge  at  point  location.





2.0  Introductory remarks

It   is   not   only the problem of coping  with  an   immense  worldwide  problem  of  increasing  demand  of  water  that  has  to  be  faced but  also   equally  daunting  is  the  problem of  producing  a  consistent body  of   hydrological  theory  that  will  be  scientifically consistent and  useful   both   for   the   planning   of  data  measurements  and  the solution of   problems   in the   real   world (Doogee, 1988).   Keeping  this  problem  in  view  a  review  of  literature  is  modeled on  rainfall  periodicity   and groundwater recharge.

2.1               Studies on rainfall periodicity

2.1.1         Introductory remarks

The   method   of  analysis   of   the   periodicity   of   rainfall evolved through human beings’  continuous  strides over predicting any changes  in  climate  which passed  through  speculation  based  on past experiences  in  the  mythological  period ; postulations  and  hypotheses in   the   ancient   historical   periods;   and   indexing,   probability, correlation  and  regression  studies  and  some  trials  on  physically based models  in  the  recent years.

2.1.2    Prediction of   rainfall   during   mythological and ancient  historical periods   India,   the land of   Monsoon,   has her tradition to study the  rainfall from the  time  immemorial.   During   1200   and    500    BC  or     6000   and 4000     BC  in  Rg-Veda,   the  oldest  literary works of  the  Aryans  settled on  coming  to   India,   there   is  the  description  of  what  could  be  the monsoon   rains   in  the  north-west  India  though  the  Word  Monsoon was coined  much   later  and  that  information was  pointed out by an Indian scholar,   M.V.Unakar in  his  treatise  nearly  fifty  five years  ago. There   is  also  mention  of  the  return  of  a  rain-time,   the rainy  season  of  the  year.  The   fact  that   there  was  period  when  it  rained  heavily  every  year  was  observed  by the   early  Aryan  settlers in  India (Das, 1988).   By  the  fourth   century  BC during  the  reign  of  the Maurya  in India   in  the   book  of   Kautilya   Arthasastra,  there   is  details  for measuring   rains  and  the   reference of using   rain gauge and there was attempt  of  forecasting  of  such  rainfall   by  observing  the   position, motion  and   pregnancy (garbhadhana)   of  Jupiter;   the  rise,   set   and  motion  of  Venus  and  the   natural   and  unnatural   aspect  of  the   Sun  (Shastri,1919and 1923; and Chattopadhyay,1982).  During  the   contemporary   period   of   Kautilya, in  a  comprehensive  text  on   agricultural   science  Kasyapamuni  Kathita  Kasyapiya  Krishi  Sukti  assigned  to  Muni  Kasyapa  there   is  a  mention  about   the   desirability   of   waiting   for   the   Monsoon   to   take   up  agricultural  operations    (Raychawdhuri  and Kaw,    1964;   and Ashok  Raj, 1979)  and  according  to  Wilson (1835)  and   Garrett (1871)  Kasyapa  lived   during  the  fourth century  BC  in  India.   In  the  Christian   Bible  there  is mention   of  a  period  of  seven  good  years  followed  by  seven  years  of   famine   in  Egypt  (Borley, 1989).   In the  later periods  there  occur descriptions  of  the Monsoon in  the  early  history  of  countries  which  had  a  maritime  interest  over the  Arabian  Sea  and  the  neighbouring  parts  of  the  Indian Ocean.  There occurs a   description of the Monsoon in the Periplus of the Erythrean Sea written about 60 AD  by  an  unknown  Greek  sailor.  A periplus is a navigators’  pilot   book,  and  Erythrean  Sea   was  the  name  given  by  the ancient  Greeks  to  the  Red  Sea,  the  Persian  Gulf  and  the  Arabian  Sea (Das,1988).   Around 400 AD  Fa Hsien,   a   Buddhist  scholar  visited  India  from  China,   referred  to  the  winter  Monsoon  along  the  east  coast  of  India  in his writings,  Record of the Buddhist Kingdoms (Das, 1988).   In  India  Kalidasa,  a contemporary  of  Fa Hsien,  perhaps most  beautifully  described  the  appearance  of  monsoon  clouds  in  his  Sanskrit  classic,   Meghdootam  around  fourth  century  AD.   In  his  book  Kalidasa  described  the  arrival  of  the  monsoon  at  Ujjain (in  Madhya  Pradesh  State)   on  the  first  day  of  Asadha (15 June)  which   is surprisingly  similar with the   present  arrival  of  monsoon rains  over  that  part of  India (Das, 1988)  and  considering  the  changes  in  the  climate  this  fact  may  lead  to  a  postulation   on  the  periodic  nature  of  rainfall.           There is  a book extant  called   Krsi-Parasara bearing  on  the subject  of  agriculture  and  there  are  the  sayings  of  the  mythical Khana  full  of  practical  suggestions  that  are  found  useful  even  today (Eder, 1964, 1966 and 1970; Rama Raju, 1976;  Ali, 1979;   Majumdar, 1982). Krsi-Parasara is  of  uncertain  date  but  was  composed  of  not later than  fifth  century AD.  A translation of  the  Bengali  edition  of that  book  has  been  published  by  the  Rothamstad  Experimental  Station in the   form  of  a  bulletin (Chattopadhyay, 1982). The time of Khana was  not  more  than  four   hundred  years  ago,   but  there  is  conspicuous similarity among  some  of  her  works  with  those  of   Varahamihira   of  nearly   one  thousand  and  five  hundred  years  ago (Vidyaratna,1900; Kar, 1929; Bandyopadhyay,1967 and 1973;and Chattopadhyay, 1982).         Near   about the   tenth   century AD,   Al  Masu’di, an  Arabian  geographer  from  Baghdad,  gave  accounts  of  the  reversal  of  ocean  currents over the  Indian Ocean in his book,  Meadows of gold and mines of gems(Das,1988).

2.1.3               Recent studies          In the  wake  of predicting any trends  in the   climatic change the  studies  in  the  recent years evolves the methods  like formulation of  indexes,   studies  on  probability  of  occurrence,  studies  on correlation  and  regression  of  rainfall  over  other  climatic  factors, physically   based   models and the studies on periodicity.                 Formulation of indexes        The   occurrence   of drought   and flood has   a tendency to  create  an  impression  regarding  the  setting  up  of  a  trend  in  the rainfall of a  region.   The climate of any place   is   the composite  weather condition by averaging the atmospheric elements like rainfall  over  a  long  period   of time  say thirty years or more.  An usual event  like   flood  or  drought  is  very  unlikely  to  change  such  values (Das, 1988)   like drought index (Kalyanasundaram  and   Ramasastry, 1970),  CAFEC   (Climatically Appropriate For Existing Condition) precipitation (George et  al.,1973),   climatic crop  growth  indices (Das,1976),   or  effective rainfall (Cocheme and Franquin, 1967;  Virmani, 1975;  Morris  and Zandstra, 1978;  Ashok Raj,1979;  Stern  et  al., 1981 and  1982), precipitation concentration index (PCI) over  Asia and  regional  division by  Sato  et  al. (1985)  and  assessment of   agricultural  drought from soil moisture deficit by   George and Ramachandran (1970)  and areal  extent of  south-west monsoon   droughts in India by George  et al. (1975).      Mindling (1944) studied  the  occurrence  and duration of dry  periods,   using  a  total  of  one  inch of precipitation  as  the criterion  for  the  end  of  a drought.  The  hydrological  excess,  flood  and   droughts   were   identified  following  Oliver’s  precipitation concentration index using triad rainfall for the season June through September  for  the  period 1901-80  of  360  selected  stations (Singh  et  al.,      1988)  and  the  onset of monsoon rainfall patterns   in India was  studied by Sreekesh and   Sivasami (1988).                 Studies on probabilistic nature of rainfall            Studies on the estimates of probable rainfall were done by  Thom  (1966), Engman and   Hershfield (1969), Diskin (1970), Raman et al., (1970),  Battan  and Green (1971),  Duckstein  et al.            (1973),  Doorenbos  and Pruitt (1975),  Hanson  et  al. (1980),   Vines  and  Tomlinson (1980),  Hanson       (1982),  French (1983),  Tung (1983), Osborn (1984, 1987),  Woolhiser et al.(1985),  Goel (1987),   Sivaramakrishnan and Sridharan (1988) and others.      Hershfield and Wilson (1960)  studied on the comparison of extreme  rainfall  depths from   tropical and subtropical storms; Huff and Changnon (1963) published an elaborate study of drought frequency in   Illinois,  which centered attention on the frequency and duration of periods of drought weather; maximum possible rainfall at a station was  studied  by  Ranga Rao (1967);  distribution  function for seasonal and annual  rainfall   over India was studied by Mooley and Rao (1968);  Jenkinson        (1969)  studied  on  the  estimation  of  maximum  floods;  forecasting of heavy rain was done by   Raman et al. (1970);  rainfall patterns over India and adjacent seas were studied by Ananthakrishnan and  Pathan (1971);   Kazman (1972)   elaborated  the   importance  of preparing   the   maps showing   the frequency of droughts to determine the  need  for  a  supplemental irrigation in humid areas and the need for  large  reservoirs   to supply adequate water to concentrations of people  and   industry and for crop production during drought periods; Victor and Sastry (1979)  studied the dry spell probability by Markov Chain  Model  and  its applications to crop development stages; NERC (1975)  published  report on flood studies;  Vanniasingam and Shaw (1978)  studied  on  rainfall  depth-duration-frequency for Sri Lanka; short  period  fluctuations   of New Zealand rainfall   were studied by Tomlinson   (1976);  the  possibility of using the non-seasonal rainfall  as  a parameter in forecasting the nature of annual rainfall was found  out  by  Sivaramkrishnan (1983);   Goel      (1984)  studied  on   probable rainfall  for  integrated planning;  fluctuations in All-India   summer  monsoon   rainfall  during 1871-1978 were  studied  by  Kooley and  Parthasarathy (1984);  Sreedharan  and  James (1988, 1990)  studied  on  the  rainfall  frequency analysis for western ghats region and the  Periyar   basin  of  Kerala  in   India;   probability  analysis  of  annual  rainfall  of Orissa was   done to   study the   probability  of  occurrence   for  effective  water-harvesting  and water   conservation  structures by Sharma et al. (1988);  Dhar and Nandargi (1989)  studied  the  severe  rainstorms  of contiguous  Indian states;  Rao (1990 a, b) studied the loss rates for application to severe rainfall storms and  on temporal distribution of design storm rainfall.                Correlation and regression studies           A good number of   attempts have been contributed to focus  on  the  climatic  trend through studies on correlation and regression  of  rainfall over other climatic factors.           As  for example,  correlation   approach in seasonal variation  in climate (Walker, 1908);  Upper air correlation (Mahalanobis, 1922);  correlation  and  variation  of  normal  rainfall  for July, August and  September  in North Bengal (Mahalanobis, 1923 a,   b);   statistical  studies  in meteorology          (Mahalanobis, 1924);   rainfall  in  relation to  floods  in  north Bengal (Mahalanobis, 1926      a,   b) ;   correlation  between  the  height of Brahmani at Jenapore in Orissa and the rainfall in the catchment  area  (Mahalanobis, 1933);   precipitation  and  percentage   of  runoff  in the Mahanadi  in Orissa            (Mahalanobis and Chakravarti, 1933); correlation of rainfall during rain storms in the Mahanadi catchment (Mahalanobis  and Nag, 1933);   exact  test  of  association  between  the occurrence of thunderstorm and upper air ionization (Mahalanobis and  Bose, 1937 a,   b);   seasonal  forecasting  in  India (Savur, 1933);  characteristic  feature of rainstorms and river floods  in Orissa (Mahalanobis, 1940 a,   b);  regional variation  of  rainfall  in Britain (Reynolds, 1953;  Gregory, 1956) ;  systematic variations   in the annual  rainfall  over  certain parts of  India (Pramanik  and  Jagannathan, 1953);  fluctuations of  wet   and   dry   years  analysed  by  serial  correlation (Friedman, 1957);   prediction  of  long-continuing  drought  in  south  and  south-east Texas ( Yevjevich, 1964);   secular  variations  of  regional  rainfall  over India          (Parthasarathi  and Dhar, 1974);  effects   of  urbanisation  on  precipitation (Rao  and  Rao, 1983); hydroclimatic  fluctuations  of the  upper Narmada catchment   and its association with break-monsoon days over India (Singh et al., 1988); the  seasonality  of  monsoon  rainfall  distribution in Bangladesh for its  association with   the seasonal changes in soil moisture, surface flow  and  groundwater  level  to  determine  the  irrigation requirement as  well  as  capacity  during  the drier  months and to tune the crop calender  with  the  arrival  and departure of monsoon (Shamsuddin  and Alas, 1988);   diagnostic  study  of  south-west  monsoon (Singh  and  Thorat, 1988);   rainfall  and  flood  study of  1989     monsoon  season  over  contiguous  India (Dhar and Nandargi, 1990).

                                ——to be continued