﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  97 
  

  

  Francisco, 
  + 
  9 
  per 
  cent 
  and 
  — 
  10 
  per 
  cent. 
  For 
  a 
  25 
  year 
  period, 
  

   it 
  was 
  found 
  that 
  the 
  extreme 
  variation 
  was 
  10 
  per 
  cent, 
  both 
  

   at 
  St 
  Louis 
  and 
  New 
  Bedford. 
  Mr 
  Henry 
  reached 
  the 
  conclusion 
  

   that 
  at 
  least 
  35 
  to 
  40 
  years' 
  observations 
  are 
  required 
  to 
  obtain 
  

   a 
  result 
  that 
  will 
  not 
  depart 
  more 
  than 
  ± 
  5 
  per 
  cent 
  from 
  the 
  

   true 
  normal. 
  The 
  average 
  variation 
  of 
  a 
  35 
  year 
  period 
  w^as 
  found 
  

   to 
  be 
  ± 
  5 
  per 
  cent, 
  and 
  for 
  a 
  total 
  40 
  year 
  period 
  ± 
  3 
  per 
  cent. 
  

  

  This 
  preliminary 
  study 
  indicates 
  slightly 
  more 
  range 
  than 
  was 
  

   found 
  by 
  Mr 
  Binnie, 
  although 
  it 
  may 
  be 
  remembered 
  that 
  the 
  

   observations 
  of 
  the 
  latter 
  are 
  far 
  more 
  extensive 
  than 
  Mr 
  Henry's. 
  

  

  Again, 
  since 
  the 
  runoff 
  is 
  a 
  function 
  of 
  the 
  rainfall, 
  it 
  follows 
  

   that 
  it 
  must 
  be 
  affected 
  in 
  some 
  degree 
  in 
  a 
  similar 
  manner. 
  As 
  

   to 
  just 
  the 
  relation, 
  so 
  far 
  as 
  known, 
  very 
  few 
  computations 
  have 
  

   been 
  made. 
  Indeed, 
  very 
  few 
  runoff 
  tabulations 
  are 
  extant 
  which 
  

   are 
  long 
  enough 
  to 
  settle 
  this 
  question. 
  It 
  is 
  clearly, 
  therefore, 
  

   very 
  difficult 
  to 
  solve 
  definitely 
  so 
  abstruse 
  a 
  problem 
  as 
  that 
  of 
  

   the 
  extent 
  to 
  which 
  forests 
  affect 
  rainfall. 
  All 
  solutions 
  are 
  

   necessarily 
  tentative 
  in 
  their 
  character 
  and 
  will 
  be 
  for 
  some 
  time 
  

   to 
  come. 
  

  

  Minimum 
  precipitation 
  in 
  New 
  York. 
  Let 
  us 
  now 
  examine 
  as 
  

   to 
  what 
  the 
  records 
  of 
  precipitation 
  in 
  New 
  York 
  indicate 
  in 
  

   regard 
  to 
  the 
  probabilities 
  of 
  extreme 
  low-water 
  periods. 
  The 
  

   following 
  records 
  of 
  minimum 
  precipitation 
  are 
  herewith 
  in- 
  

   cluded 
  : 
  At 
  Albany 
  the 
  water 
  years 
  1895 
  and 
  1896 
  represented 
  a 
  

   period 
  of 
  very 
  low 
  precipitation. 
  The 
  following 
  are 
  the 
  totals 
  

   of 
  the 
  several 
  periods 
  : 
  

  

  1895 
  1896 
  

  

  Storage 
  12.58 
  14.79 
  

  

  Growing 
  8.88 
  8.31 
  

  

  Replenishing 
  8.93 
  6.64 
  

  

  Total 
  30.39 
  ~ 
  29.74 
  

  

  The 
  total 
  precipitation 
  of 
  the 
  previous 
  year, 
  1894, 
  was 
  34.45 
  

   inches. 
  It 
  is 
  probable 
  that 
  for 
  the 
  water 
  year 
  1896 
  streams 
  in 
  

   the 
  vicinity 
  of 
  Albany 
  did 
  not 
  run 
  to 
  exceed 
  9 
  inches 
  on 
  the 
  catch- 
  

   ment 
  area. 
  

  

  