.onAttach: no visible global function definition for
  'packageDescription'
hargreaves: no visible global function definition for 'is.ts'
hargreaves: no visible global function definition for 'frequency'
hargreaves: no visible global function definition for 'ts'
hargreaves: no visible global function definition for 'start'
hargreaves: no visible global function definition for 'cycle'
kern.plot: no visible global function definition for 'par'
kern.plot: no visible global function definition for 'plot'
parglo.maxlik: no visible global function definition for 'optim'
penman: no visible global function definition for 'is.ts'
penman: no visible global function definition for 'ts'
penman: no visible global function definition for 'frequency'
penman: no visible global function definition for 'start'
penman: no visible global function definition for 'cycle'
plot.spei: no visible global function definition for 'ts'
plot.spei: no visible global function definition for 'end'
plot.spei: no visible global function definition for 'frequency'
plot.spei: no visible global function definition for 'start'
plot.spei: no visible global function definition for 'par'
plot.spei: no visible global function definition for 'plot'
plot.spei: no visible global function definition for 'polygon'
plot.spei: no visible global function definition for 'abline'
plot.spei: no visible global function definition for 'grid'
plot.spei: no visible global function definition for 'lines'
plot.spei: no visible global function definition for 'points'
spei: no visible global function definition for 'is.ts'
spei: no visible global function definition for 'ts'
spei: no visible global function definition for 'frequency'
spei: no visible global function definition for 'start'
spei: no visible global function definition for 'window'
spei: no visible global function definition for 'embed'
spei: no visible global function definition for 'cycle'
spei: no visible global function definition for 'sd'
spei: no visible global function definition for 'qnorm'
spei: no visible global function definition for 'pnorm'
thornthwaite: no visible global function definition for 'is.ts'
thornthwaite: no visible global function definition for 'frequency'
thornthwaite: no visible global function definition for 'ts'
thornthwaite: no visible global function definition for 'start'
thornthwaite: no visible global function definition for 'cycle'
Undefined global functions or variables:
  abline cycle embed end frequency grid is.ts lines optim
  packageDescription par plot pnorm points polygon qnorm sd start ts
  window
Consider adding
  importFrom("graphics", "abline", "grid", "lines", "par", "plot",
             "points", "polygon")
  importFrom("stats", "cycle", "embed", "end", "frequency", "is.ts",
             "optim", "pnorm", "qnorm", "sd", "start", "ts", "window")
  importFrom("utils", "packageDescription")
to your NAMESPACE file.