1.   Purpose and objectives

     Information on the frequency of occurrence of multi-year drought sequences is fundamental to the formulation of effective strategies for managing droughts. However, the analyses required to estimate the probability of occurrence of multi-year droughts are quite complex and this program assists in these analyses.

2.   Description

     DROUGHT is a user-friendly PC-based program, which allows the estimation of the probability of occurrence of droughts of any duration, including multi-year droughts. It performs partial duration frequency analyses of overlapping and non-overlapping n-month low flow sequences. Details of the methodology used in these analyses can be found in Section 3-7 of the publication River and Reservoir Yield by T. A. Mc Mahon & R. G. Mein, Water Resources Publications, 1986.  The cumulative probability distribution of low flows is obtained from the steady-state solution of the class transition probability matrix.  The results of this program may be used to calculate other statistics such as the average recurrence interval (ARI). 

     The program also allows for the plotting of the results. It has an in-built README file, which describes the inputs and outputs, actual use of the program, and provides a worked example.

3.   Input

     The name of a monthly streamflow data file; the start year and month of the streamflow sequence; whether overlapping or non-overlapping sums are to be used to construct the transition probability matrix; and the length of the n-month drought sequence to be processed.

4.   Output

     A low flow frequency plot is displayed on the graphics screen and may be saved as a plot file. The on-screen results are written to a user-specified output file.

5.   Operational requirements and restrictions

     The system hardware requirements for operation of the software are as follows:

     * an 80386-, 80486- or Pentium-based IBM compatible personal computer;
     * an Intel or compatible math coprocessor;
     * PC-DOS or MS-DOS Version 3.3 (or Compaq DOS 3.31) or higher; a VGA
       or SVGA monitor.

6.   Form of presentation

     IBM PC-based computer program on disc with users guide.

7.   Operational experience

     Program has been used within Australia, primarily by Government Departments and water authorities in the State of Victoria to assist in the development of Drought Management Plans.

8.   Originator and technical support

     The program was developed by Mr R. Nathan (now of Sinclair Knight Merz (SKM)) for the Water Bureau, Department of Natural Resources and Environment (NRE), Victoria.  Questions about the program should be directed to the Water Bureau.

9.   Availability

     From the HOMS National Reference Centre for Australia.

     The program is only available to government departments/agencies and water authorities and educational institutions and must not be used for commercial gain.

10.   Conditions on use

      Users of the program are required to complete, sign and return to the Water Bureau, a "Terms and Conditions of Supply" form acknowledging that:

      * the performance of the DROUGHT software is not guaranteed;
      * NRE and SKM are not liable for any damage arising from the use  or 
        abuse of DROUGHT software;
      * the software and associated documentation may be copied and used
        only by the organization completing the form.