REQUERIMIENTOS OPERATIVOS

The  next  actor  upstream  from  the  millers  is  the  Food  Reserve  Agency  (FRA),  an  overview  of   the  corresponding  model  structure  is  visible  in  figure  10.  

Figure  10:  FRA  structure  

FRA  has  different  kinds  of  storages  in  many  locations  around  Zambia.  Farmers  first  bring   their   maize   to   the   nearest   local   FRA   sales   point,   which   normally   consists   of   temporary   storage   facilities,   such   as   slabs.   These   facilities   are   usually   not   well   protected   and   thus   exhibit   high   loss   ratios.   Maize   is   then   moved   from   there   to   satellite   storages   in   regional  

centres,  which  feature  more  elaborate  permanent  storage  facilities,  such  as  sheds  and  silos.   Sheds,  however,  still  have  quite  high  loss  ratios  in  the  medium  term  and  only  silos  really   keep  maize  largely  unaffected  by  pests,  moisture  and  fungi.  (Bou  Schreiber,  2015)  

I   therefore   assume   that   FRA   puts   as   much   maize   into   their   silos   as   their   silo   capacity   allows.  Once  these  are  full,  the  next  best  storage  option  is  to  put  the  maize  into  the  sheds.   And  only  if  these  are  also  already  full  (something  that  only  occurred  in  the  bumper  harvest   years   2010-­‐14   when   FRA   bought   very   large   amounts   of   maize),   maize   is   left   in   the   local   slab  structures.    

Building  a  model  structure  that  could  adequately  measure  the  maize  loss  in  FRA  storages   proved   to   be   one   of   the   trickiest   parts   of   the   work.   After   experimenting   with   different   solutions   it   became   increasingly   clear   that   I   could   not   work   with   the   traditional   way   of   measuring   residence   times   (dividing   a   stock   by   its   outflows),   because   the   strong   seasonality   of   my   model   lead   to   extreme   fluctuations   in   the   residence   time   that   did   not   yield   any   realistic   values.   I   thus   adapted   the   age   measurement   structure   from   Bou   Schreiber  (2015)  which  proved  to  work  well  despite  the  seasonality  in  my  model.  It  works   the   following   way:   when   new   maize   is   purchased,   the   current   time   (in   months)   is   multiplied  by  the  purchase  volume  (in  weight),  and  the  thereby  “age-­‐tagged”  maize  volume   is  accumulating  in  the  co-­‐flow  structures  visible  in  figure  10  above  the  value  chain  flows.   Thus,  dividing  the  maize  currently  on  storage  by  the  accumulated  age-­‐weight  stock  in  the   co-­‐flow  returns  the  average  time  when  the  maize  on  storage  came  into  the  stock  (average   entry  time).  

As  maize  is  sold,  old  and  new  maize  are  assumed  to  be  mixed  for  sale,  so  that  on  average,   the  maize  sold  (or  moved  to  better  storage  facilities,  in  case  of  the  first  FRA  stock)  has  the   average   age   of   all   the   maize   in   store.   This   procedure,   as   opposed   to   e.g.   selling   only   the   oldest  maize  first,  is  followed  because  the  longer  maize  is  on  storage,  the  more  its  quality  is   adversely  affected  by  moisture,  fungi  etc.  –  and  the  stronger  quality  is  affected,  the  lower  is   the  price  for  which  the  maize  can  be  sold.  Therefore,  old  maize  is  mixed  with  newer  maize  

in  order  to  be  able  to  sell  it  for  a  good  price.  For  more  details  on  this,  see  Bou  Schreiber   (2015).  The  outflow  from  the  age-­‐weight  co-­‐flow  is  thus  not  multiplied  by  the  current  time,   but  by  the  average  age  (Average  entry  time)  of  the  maize  in  stock.  

Now,  to  measure  the  average  time  that  the  maize  in  stock  has  actually  spent  on  storage  (the   “relative   age”),   one   simply   has   to   take   the   difference   between   the   current   time   and   the   average   entry   time.   The   relative   age   (i.e.   time   spent   on   storage)   of   the   stock   then   determines   the   loss   ratio,   which   is   exponentially   rising   with   relative   age   to   reflect   the   exponential  effects  of  spreading  moisture,  fungi  and  pest  populations.  Multiplying  the  loss   ratio  with  the  stock  then  determines  the  actual  loss  outflow.  

Since  Bou   Schreiber's  (2015)  original  structure  was  intended  to  measure  the  losses  over   one  annual  cycle,  the  outflow  has  to  be  divided  by  12  months  in  order  to  transform  the  time   horizon  and  return  the  correct  loss  values.  In  the  case  of  the  permanent  storage  structure,   the  combined  loss  ratio  also  depends  on  which  ratio  of  the  maize  is  in  silos  and  which  ratio   is  in  sheds,  since  the  two  storage  types  exhibit  distinctly  different  loss  ratios  (cf.  appendix   C.3).  

FRA   then   sells   its   maize   according   to   domestic   demand   to   contracted   millers,   but   not   to   retailers  or  consumers  (N.  M.  Mason  &  Myers,  2011).  This  is  important  since  it  means  that   maize  once  purchased  by  FRA  is  effectively  locked  up  in  the  formal  value  chain  and  cannot   be   supplied   to   informal   consumers   any   more.   If   there   is   still   excess   maize   left   in   FRA’s   storages  at  the  end  of  the  marketing  year  and  it  cannot  be  sold  domestically,  FRA  exports   the   amount   exceeding   its   desired   security   stocks.   For   more   details   on   these   exports,   see   section  4.3.4.  

Furthermore,  I  assume  that  FRA  wants  to  keep  a  certain  share  of  security  stocks  to  fulfil   their  original  mandate,  which  is  stabilizing  the  maize  price  with  strategic  maize  reserves.   However,  I  included  a  switch  structure  that  sets  the  desired  reserves  to  zero  when  we  have   a  year  with  a  structural  maize  deficit.  This  reflects  that  FRA,  whose  mandate  is  secure  the  

maize   supply   for   the   population,   would   not   keep   stocks   locked   up   while   domestic   consumers  demand  more  maize  to  fulfil  their  basic  needs.